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Post by howie1 on Dec 17, 2017 12:30:48 GMT
Was trying to get a comparison for ChrisV to show Baader MPCC images on 200mm F/5 vs 150mm F/4. Went 2 hours out of Brisbane to a bit past the town of Esk, but between wind bouncing the OTA around, and me being unable to bring the Canon 650d to focus in the GSO 150mm F/4, I was unable to do the comparison. Tonight was supposed to be 30% cloud around Brisbane but by 5pm we were totally socked in - satellite image attached below. Anyway, thought I'd start the thread and complete the review when weather permits. Watch this space/thread. But, when setting up and aligning with my trusty ol' 200mm f/5, I did manage to snap off NGC2070 and M42. Excuse the slightly elongated wobbly stars due to the strong winds out there bouncing the big 8" Newt around on the HEQ5. Here's the two single 30 second ISO800 shots from the Canon mounted on the 200mm F/5 and stretched/displayed in Astrotoaster and saved to disk. Low hanging fruit (as they say) but always fun if they're up when setting up and checking goto's and such. And at 30 sec + 15 for Toaster to do its stuff, very quick to check out. Site near Esk ... M42 ... NGC2070 ... This arvo's weather (big cloud moving up from the South towards Brisbane) ...
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Post by ChrisV on Dec 17, 2017 12:45:26 GMT
Never get tired of seeing those beautiful single sub minute shots Howie. Better than half the AP stuff on IIS with hours of stacked/processed data.
At F4 it'll be 15sec subs!!
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Post by howie1 on Dec 17, 2017 12:55:33 GMT
Oh yes ... so why'd I title this thread "Testing F ratio - fact or myth" rather than "Testing MPCC on 150mm f/4 Newt"? The reason is on my 200mm Newt I can defocus and immediately see a bright round blob in Canon Liveview which is at 25 fps video straight from the camera. I do all my alignments using Canon liveview and centre the stars using 25 fps live video feed. But ... I racked right through the GSO 150mm Newts focal range and did not see anything at all on Liveview. It was totally black. At 150mm compared to 200mm aperture the GSO 150mm is getting approx 44% less light gathering aperture. But, the GSO is at f/4 compared to f/5 for the other OTA, and so it should have been 36% brighter. And 36 and 44 are not that far off from each other and should have compensated ... at least I thought so. I figured I should have at least seen a defocussed blob. But I saw nothing! I've read in the past posts on AP'ers going on about the F ratio "myth" but couldn't really understand their formula and answers and charts n stuff. But I remembered the statements regarding F ratio "brightness" of image with a camera on a scope (instead of a camera lens) as being a myth. So, it made me extremely suspicious that the smaller 150mm just wasn't letting enough light get to the sensor to see anything at all. And ... yes, I did check I had taken the cap off! Plus I also shone a light down the tube to check the camera, usb, liveview app were all actually not frozen/crashed! It could have been some other glitch ... guess we'll know next time its clear and I can get out and do the comparison properly to show the MPCC at work at f/5 and f/4, as well as figure out for myself with an actual in-field experiment the F Ratio - myth or not question!
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Post by howie1 on Dec 17, 2017 12:58:53 GMT
Never get tired of seeing those beautiful single sub minute shots Howie. Better than half the AP stuff on IIS with hours of stacked/processed data. At F4 it'll be 15sec subs!! Thanks Chris ... sometimes I wonder if the Canon is somehow "broken" ... but in a good way! It just seems to be magic on the SW 200p newt. As per post I just made before .... I am really scratching my befuddled head as to why the 150mm f/4 liveview was just black? Like I said ... next time out it will be a very, very interesting experiment! And yes, I'd love to see 15 sec at f/4 ... if that F Ratio 'thing' actually works (says a now doubting Howie!).
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Post by Dragon Man on Dec 17, 2017 13:32:01 GMT
Fantastic results Howie! The 'imaging experts' would complain about the noise, but as we know, they are missing the point
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Post by howie1 on Dec 17, 2017 20:22:34 GMT
Fantastic results Howie! The 'imaging experts' would complain about the noise, but as we know, they are missing the point Thanks Ken. Yup, out in the dark on a small laptop screen just slewing around 'stuff' ... Noise? What noise?
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Post by ChrisV on Dec 17, 2017 22:50:23 GMT
That F ratio as myth comes from articles by Craig Stark or Stan Moore. Is an interesting read. It kind of makes sense after a few reads. Here's one www.stark-labs.com/help/blog/files/FratioAperture.phpIs it just a really narrow focus range on the F4. So you just miss it if going through too fast?
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Post by howie1 on Dec 18, 2017 0:12:42 GMT
That F ratio as myth comes from articles by Craig Stark or Stan Moore. Is an interesting read. It kind of makes sense after a few reads. Here's one www.stark-labs.com/help/blog/files/FratioAperture.phpIs it just a really narrow focus range on the F4. So you just miss it if going through too fast? I'm sure you're right Chris ... in the dark and not having a clue where the faster and smaller f/4 focal point was, I blew right through it. On the Stark article ... ta. First read just now ... err ... embarrassed to say that I think I'm going to have to have another couple of reads Or, Wednesday night forecast looks ok and just get out there and crack on with a test.
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Post by Deleted on Dec 18, 2017 0:19:18 GMT
Chris That article is good reading. With the gso 150 f4 I seem to need just a little bit of extension on the focuser with the 294 so I add either my .8 or .6 reducer which makes focus around 3.6 on the focuser . I suppose I am breaking rules here as the reducers are meant for refractors with f6 or more but they seem to work ok and saves me messing around with extensions. Paul
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Post by howie1 on Dec 18, 2017 1:15:49 GMT
Chris That article is good reading. With the gso 150 f4 I seem to need just a little bit of extension on the focuser with the 294 so I add either my .8 or .6 reducer which makes focus around 3.6 on the focuser . I suppose I am breaking rules here as the reducers are meant for refractors with f6 or more but they seem to work ok and saves me messing around with extensions. Paul Thanks Jaybee, re a bit of extension required for the 294 ... that makes sense. Ta. As when I focused in the daytime, the Canon DSLR reached focus at 46 (mm?) on the GSO focusers etched 'scale'. The max extension was at 50 on the scale ... so waaaaay outwards ... just 4mm short of fully outwards extension. Given the Canons sensor's 26mm diagonal measurement is slightly larger than the 294's diagonal 23mm measurement ... one would expect the Canon reaches focus a tad more inwards than you've found with the 294 (which needed a slight extension). And that's the case. So all confirmed. Thanks. Makes me think they made the 6" GSO to handle full frame sensors IE lots of inwards travel ... and so now I am wondering "I wonder what a good full frame camera would shoot on that sucker?!?!?" LOL. Cheers.
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Post by ChrisV on Dec 18, 2017 2:31:27 GMT
You know you need a Sony A7S ...
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Post by Deleted on Dec 18, 2017 7:52:47 GMT
Interesting to throw around a few figures from the Stark-labs article. I have a cheapo SW 120 F5 refractor which is virtually never used.It has the same FL and image scale as the 150 f/4 newt. The secondary mirror of the newt is 63mm or about 2.5 " as per article. That makes the effective aperture of the 150 = 5.45 inches.That equates to 1.34 times more CCD photons for the Newt. Using the 76% light passing for 2 mirrors then 76% of 1.34 is about 1. So the number of photons hitting the 294 for the 120 refractor and the 150 reflector should be about the same. Then we have all the other factors of read noise, F ratios,and other stuff he mentions so I'm still not sure how the 2 scopes will compare. I will add that to the list of things to do. Paul
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Post by howie1 on Dec 18, 2017 12:10:14 GMT
Interesting to throw around a few figures from the Stark-labs article. I have a cheapo SW 120 F5 refractor which is virtually never used.It has the same FL and image scale as the 150 f/4 newt. The secondary mirror of the newt is 63mm or about 2.5 " as per article. That makes the effective aperture of the 150 = 5.45 inches.That equates to 1.34 times more CCD photons for the Newt. Using the 76% light passing for 2 mirrors then 76% of 1.34 is about 1. So the number of photons hitting the 294 for the 120 refractor and the 150 reflector should be about the same. Then we have all the other factors of read noise, F ratios,and other stuff he mentions so I'm still not sure how the 2 scopes will compare. I will add that to the list of things to do. Paul Paul, if you do manage to do a test, it will be interesting to see what transpires. Cheers
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Post by howie1 on Dec 18, 2017 12:11:11 GMT
You know you need a Sony A7S ... You know there's one on IIS for $1500 ... !!!
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Post by ChrisV on Dec 18, 2017 12:38:08 GMT
Yes. I was waiting to see you buy it
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Post by howie1 on Dec 18, 2017 23:30:51 GMT
Yes. I was waiting to see you buy it LOL ... Unfortunately no, Chris. These sorts of things always happen to me! Don't see one come up at decent price for years ... then when I have to spend the cash on some other more important things, the desired object comes up at decent price!
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Post by Deleted on Dec 19, 2017 5:23:48 GMT
"Went 2 hours out of Brisbane to a bit past the town of Esk,"
Howie - If you are heading out that way, you are welcome to come to my place.
I'm on 5 acres at Cedar Grove (about halfway between Esk and Mt Hallen).
Dark blue zone according to Dark Site.
Robert
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Post by howie1 on Dec 20, 2017 4:09:06 GMT
Thank you Robert. Very much appreciated. Beautiful part of SE Qld and the skies were nice and dark that's for sure.
Regards Howie
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Post by howie1 on Jan 8, 2018 21:55:14 GMT
Well I got a Rokinon f2.0 135mm focal length lens for my Canon DSLR's for Xmas, and on Sunday night I went to try it out. Sorry Chris, I did not have time to test the f/4 6" Newt. My bad. Summarising: I found the f2.0 67mm aperture (as near as I can tell it's 67mm) Rokinon 135mm FL lens required the same Astrotoaster settings in order to yield a similar "brightness" of image. But needed slightly longer shots! This is taking into account the image scale of any nebula is much smaller with the 135mm Focal Length lens compared to the 1000mm FL of my f5.0 Newtonian. I tried to get the brightness of much smaller M42 or Eta Carina nebulosity taken with the 135mm lens to be about the same as the nebulosity brightness I see in a much larger image using my 1000mm Newtonian. IE if you do the math, the area of the Rokinon lens is about 9 times smaller, but because f2.0 is about 6 times faster than f5.0 the shots have to be about 1.5 times longer at the same ISO. And this is exactly what I found. Attention ChrisV ... this (IMO) yields to you the effect of comparing your f5.0 200mm Newt and the exposure times etc you can expect on the 150mm f/4 you are thinking of. IE 1.5x faster in F Ratio but 70% less aperture area/photons captured, so you'll have to go longer with the 150mm f4.0 Newt! Still doesnt show the impact of vignetting etc so if you still want me to go try it out, let me know ... but given the bad weather and such you will probably get sick of waiting and go buy one in the meantime! LOL Normally I shoot single 30 second ISO800 jpeg images. So the images below are single 90 second unguided ISO800 jpeg images using the Rokinon lens. The Astrotoaster stretches are as shown, with Contrast and Brightness adjusted to reduce the central vignetted area so its almost black, while still allowing the object to be as bright as it can be. Post processing has been limited to Photogallery bump of shadows -I think we've all seen how in the dark the images look much brighter to your eyes on screen, compared to when you take a screenshot and look at that screenshot in the daytime where it looks quite dark and less nebulosity detail shows up. So I've tried to show close to what it looked like on screen. First image is the rig which uses a single ST80 guide ring to 'hold' the heavy lens in place (if held by a single 'camera' bolt, the camera comes loose due to the heavy lens hanging out the front and rotates under gravity when held at weird angles on an EQ mount). Then the usual 'test' objects for me M42 and Eta Carina plus the Sculptor and NGC 247 (just to the left of the adjustment window left of the Expand slider mag 9.11). I do like the nice wide field! And also the fact that I could do outreach using this lens as if I bump the ISO from 800 to 1600 it brings the exposure time down to 45 seconds and the quality wouldn't be too bad at ISO1600 ... so certainly good enough and quick enough (at 45 seconds) to do outreach showing the wide field stuff. [Edit - oh yeah ngc288 mag 8.13 globular cluster is up 10o'clock to the left of Sculptor galaxy]
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Post by ChrisV on Jan 9, 2018 23:43:57 GMT
They are really quite amazing Howie. Reckon its faster than you are saying. The dust around M42 is coming out really well - I'm sure I wouldn't see that unless I did longer exposures. And you're right, I'll probably go for a carbon fibre 8" F4 when I see one on IIS.
So you have the camera and the lens secured?
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