Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Jan 20, 2014 19:18:11 GMT
I have been really suprised by my FOV with the VRC6 and my knight owl .5x reducer. Based on this combo I should be operating a f4.5 so 685mm. However running through the FOV simulators it seems im operating more like 410mm or f 2.61. So I went to to the website for knight owl this reducer appears to need to be much closer to the sensor to get .5x. With the mallincam 1.25" adapter that comes with the camera, I'm getting more like .29x reduction. I took an image from this weekend and overexposed it, and guess what vignetting. I also noticed this when trying to push the levels to view the horsehead original image Over exposed showing vignetting Should I be worried about this. Will this hinder my views? Should I get a different focal reducer with less reduction. Looking for advise on what to do, if anything. Lee
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Jan 20, 2014 21:23:38 GMT
Hemmi you have pretty much answered my question from here astrovideoforum.proboards.com/thread/239/5-reducer-1-2-sensorI do remember you saying about using a 0.5 reducer with your jnr pro. I assumed you just had that $250 one. I made that thread as im trying to work out what the total damage is going to be if i ever invest in a 1/2" cam. Wanted to know if i had to factor a reducer into the price. Looks like i will... Question... i see there is a 2" 0.5 reducer that rock sells. But not sure if that will just be the same? I would say tho that i dont think its too much of a prob for you. As you have such a big FOV that pretty much everything will fit in your view so you wont notice anything. As nothing important will be in the corners. But for me if i had your cam even after reduction m42 wouldnt fit so i would easily notice the dodgy edges.
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Jan 20, 2014 21:50:23 GMT
Hemmi you have pretty much answered my question from here astrovideoforum.proboards.com/thread/239/5-reducer-1-2-sensorI do remember you saying about using a 0.5 reducer with your jnr pro. I assumed you just had that $250 one. I made that thread as im trying to work out what the total damage is going to be if i ever invest in a 1/2" cam. Wanted to know if i had to factor a reducer into the price. Looks like i will... Question... i see there is a 2" 0.5 reducer that rock sells. But not sure if that will just be the same? I would say tho that i dont think its too much of a prob for you. As you have such a big FOV that pretty much everything will fit in your view so you wont notice anything. As nothing important will be in the corners. But for me if i had your cam even after reduction m42 wouldnt fit so i would easily notice the dodgy edges. Well my reducer at my spacing is more like a .29x so I would think at correct spacing it should light up 100% of the sensor at correct spacing. I have been using the Owl astronomy .5x reducer for 4 years. Its cheap too! They also sell the matching c-mount to 1.25" adapter which is much shorter than the one that comes with the mallincam. I barely reach focus with just 2 of the spacers on the VRC6, the MFR5 will reach focus with all 3 spacers. So I'm differently way over the reduction factor designed for this reducer I use Here is the website for the reducer - www.owlastronomy.com/barlows.htm
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Jan 20, 2014 22:19:53 GMT
Hmmm maybe that reducer is different to the other 0.5 i have seen. it does look identical to mine but i was sure they are for ccd's only and not visual. But yours shows it on an eyepiece. So no idea sorry man i really dont know much about all this stuff. Kens your man for this! I was sure tho that most 0.5 reducers were only for 1/3" sensors. Also if you look at rocks 0.5 reducer it does say its for the 1/3" micro. You say the MFR5 will reach focus... are you saying you have one? If so im confused
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Jan 20, 2014 22:43:16 GMT
You say the MFR5 will reach focus... are you saying you have one? If so im confused No thats what rock says, He said the VRC scopes are designed to reach focus with the MFR5 with all three spacer rings (VRC spacers that go between OTA and focuser). I can't afford the MFR5, I'm sure its nice, but out of my budget right now. I have some Highpoint Scientific .5x reducers also which I may try at a latter date. Yes hoping Ken can comment on this question: Am I over reducing? Is the vignetting an issue? is this limiting my ability to catch photons? etc.
|
|
|
Post by johnno on Jan 20, 2014 23:19:45 GMT
Hemmi, I would try again with the same FR and this time try and get the exposure right and then take a snapshot of image and see if it makes any difference, maybe because its way over exposed its showing vignetting, maybe with a faster exposure, vignetting might not show up as much.
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Jan 21, 2014 1:05:53 GMT
You say the MFR5 will reach focus... are you saying you have one? If so im confused No thats what rock says, He said the VRC scopes are designed to reach focus with the MFR5 with all three spacer rings (VRC spacers that go between OTA and focuser). I can't afford the MFR5, I'm sure its nice, but out of my budget right now. I have some Highpoint Scientific .5x reducers also which I may try at a latter date. Yes hoping Ken can comment on this question: Am I over reducing? Is the vignetting an issue? is this limiting my ability to catch photons? etc. Hi Hemmi,
Not sure about your scope but with my C11 I got vignetting when I used to many spacers. I have the MFR5 and when I added and 10 and 5mm spacer I had problems. With just the 10mm spacer it seems fine but I need to do more testing on this.
The image before this one shows you what I got with all spacers!
groups.yahoo.com/group/mallincam/photos/album/1694624433/pic/1577254138/view?picmode=&mode=tn&order=ordinal&start=1&count=20&dir=asc
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Jan 21, 2014 1:38:43 GMT
No thats what rock says, He said the VRC scopes are designed to reach focus with the MFR5 with all three spacer rings (VRC spacers that go between OTA and focuser). I can't afford the MFR5, I'm sure its nice, but out of my budget right now. I have some Highpoint Scientific .5x reducers also which I may try at a latter date. Yes hoping Ken can comment on this question: Am I over reducing? Is the vignetting an issue? is this limiting my ability to catch photons? etc. Hi Hemmi,
Not sure about your scope but with my C11 I got vignetting when I used to many spacers. I have the MFR5 and when I added and 10 and 5mm spacer I had problems. With just the 10mm spacer it seems fine but I need to do more testing on this.
The image before this one shows you what I got with all spacers!
groups.yahoo.com/group/mallincam/photos/album/1694624433/pic/1577254138/view?picmode=&mode=tn&order=ordinal&start=1&count=20&dir=asc
Different spacers. I'm talking about the spacers that control infocus not the spacers that control the distance between focal reducer and sensor. these are two separate things. I have no way to control the spacing of my focal reducer to sensor distance, without buying a shorter c-mount to 1.25 adapter. What I was talking about is the big black rings in the below picture, which only control focal length. These allow a wide range of in and out focus. But these are not relevant to this topic. I just brought it up to note that I had to remove one ring to achieve focus with my reducer, but rock states with the mfr5 you can use all rings. My point was that with my current reduction factor, I need more infocus travel than the mfr5. My .5x reducer is too far away from the sensor due to its design. This gives me a greater reduction factor of ~ .29x but with a cost of vignetting. My question is, how is this hurting my views, and should i change reducers?
|
|
|
Post by Dragon Man on Jan 21, 2014 9:45:56 GMT
Lee, the best way to understand what your Focal reducer is doing, and how do reduce/enlarge your FOV or understand your FOV, it is worth reading Jim Thompson's FR test reports. He compares FOV using Mallincam and Meade FR's, using spacers, distance from sensor, etc. Some interesting results. He even combines the Mally and the Meade together. If you go to my Video Astronomy website, go to the 'Equipment' page and scroll way down to 'Resources'. After 'Books' you will see 'Focal Reduction'. There you will find links to Jim's 3 articles. But looking at your images at the start of this thread I can see clearly that your FOV is one degree. Excellent! But strange considering you should be around half a degree using that scope and a 0.5x FR. It is easy to discover your Focal reduction using two objects in a distant FOV at daytime or two stars at night time. I explain how to do it near the end of my Video here:
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Jan 21, 2014 10:08:09 GMT
You say the MFR5 will reach focus... are you saying you have one? If so im confused No thats what rock says, He said the VRC scopes are designed to reach focus with the MFR5 with all three spacer rings (VRC spacers that go between OTA and focuser). I can't afford the MFR5, I'm sure its nice, but out of my budget right now. Ahhh ok Yeh no wonder! For that price i would expect it to reach focus while still in its box! Btw i see rock sells a 0.75 reducer just for RC scopes. Not cheap either tho.
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Jan 21, 2014 12:50:13 GMT
Lee, the best way to understand what your Focal reducer is doing, and how do reduce/enlarge your FOV or understand your FOV, it is worth reading Jim Thompson's FR test reports. He compares FOV using Mallincam and Meade FR's, using spacers, distance from sensor, etc. Some interesting results. He even combines the Mally and the Meade together. If you go to my Video Astronomy website, go to the 'Equipment' page and scroll way down to 'Resources'. After 'Books' you will see 'Focal Reduction'. There you will find links to Jim's 3 articles. But looking at your images at the start of this thread I can see clearly that your FOV is one degree. Excellent! But strange considering you should be around half a degree using that scope and a 0.5x FR. It is easy to discover your Focal reduction using two objects in a distant FOV at daytime or two stars at night time. I explain how to do it near the end of my Video here: I spoke to Jim T last night, and read his focal reduction post. I'm very happy with my FOV, but not happy with the vignetting. Jim T's setup with the Meade 3.3 reducer is fantastic, He is operating at F2.8 on his VRC with zero Vignetting! I may go this route. A bit of Coma doesn't bother me, but vignetting really kills an image IMO.
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Jan 21, 2014 17:09:25 GMT
I have decided to try Jim T's method. I picked up a used Meade 3.3 reducer off of cloudy nights. And purchased all the adapters and spacers required. The large reducer should limit vignetting on the small mallincam chip.
Badder 2" to SCT Male adapter -> Meade 3.3 -> 5mm SCT spacer -> SCT 2" visual back -> 2" to c-mount adapter
Of course this line of adapters requires lots of in-focus travel, but the VRC has tons.
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Jan 21, 2014 18:01:45 GMT
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Jan 21, 2014 21:11:01 GMT
Thanks for the info, I should be right on the money. The 2" visual back is 43mm and the mallincam has a sensor distance of 12.5. So thats right at 55.5mm. Since I have the c-mount to 2" adapter for my mallincam, I dont waste any space there. And I can slide the camera out another 2.5mm if required. My setup will look almost exactly like yours, however on the OTA side of the meade 3.3 will be a badder sct to 2" adapter so it will fit into the VRC focuser.
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Jan 24, 2014 19:46:33 GMT
Here is my Meade 3.3 reducer setup. Spacing comes out 51MM (Ignore the 45mm in pic), so it looks like I will need 7mm more space. My mallincam 2 inch adapter goes all the way back to the sensor location, so It I may have to make a spacer. I will report back after I run some test.
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Jan 31, 2014 1:49:24 GMT
I tested out the meade 3.3 finally today. As pictured above I could not even reach focus with all of the focus rings removed. So i removed the little 15mm spacer between the meade 3.3 and the visual back. Now I had no trouble reaching focus with about 13mm to spare. This brings my distance to sensor to about 40-45mm. I tested it out on Polaris (something that didn't move, as i didn't want to align the mount. I moved Polaris around to all the edges of the field to test for coma, but I didn't see any odd star shapes. I have no FOV comparison yet as I only viewed Polaris, but I think this reducer will work fine.
Also no vignetting, but i didn't expect any with such a large reducer. I plan to broadcast tomorrow night so we will see how the vies look. I hope I get my mcv-1-v tomorrow to test it also. It was supposed to arrive today from jack, but i guess the weather must of held it up.
Lee
|
|