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Old 18-07-2014, 07:11 PM
kosh
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Reducers, powermates and CCD's

Hi all,
I'm looking for some advice in regards to my soon to be expanded AP equipment list.
I'm looking to graduate to mono CCD imaging and I'm not sure if certain things will work.
Firstly, I love imaging galaxies. But before I actually tried it with M83 some time ago, I didn't realise that it would be so small on the DSLR chip. Having a FL of 800mm as my longest of the two I have, I didn't really know anything about image scale before I bought my two scopes.
Anyhow, I was thinking whether I can reduce this issue using a 2x powermate to give me a focal length of 1600mm? Would this work or does it cause other issues?
The other thing, is that I am looking into an ATIK 314+ mono, and with a chip of 11.2mm diagonal, the FOV is limited. I would like to use a bintel .5 reducer to open the FOV up a bit (when imaging nebula). Would this be useable or is coma going to be an issue even with this small chip?
Also, I don't know a lot about over sampling/under sampling so any advice there would be good.
Apologies for the long post.

Goran.
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Old 19-07-2014, 01:12 PM
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PRejto (Peter)
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Goran,

You can do this but I don't think you will have enough light to avoid very long exposures if you only have 80 mm to start with. I have used a 2X Astrophysics barlow with my TEC140, so almost 2x the aperture. If you look at my site (below) the imags of M83 and M16 were both taken this way. Also over 1000mm and you probably should be using OAG.

Peter
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Old 20-07-2014, 12:09 AM
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Download the free ccd calculator by Ron Wodaski. Its very handy for seeing what the field of view will be with different telescope/camera combos including reducers, barlows etc.

The Tak 1.6Q extender is a nice piece of gear which I have used to image a galaxy with a TEC180 and KAF8300 chipped FLI Microline 8300.

It takes longer but does work.

Reducers can be tricky as they often give coma in the corners.

Greg.
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Old 21-07-2014, 05:58 PM
kosh
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Thanks for your replies guys.

Quote:
Originally Posted by PRejto View Post
Goran,

You can do this but I don't think you will have enough light to avoid very long exposures if you only have 80 mm to start with. I have used a 2X Astrophysics barlow with my TEC140, so almost 2x the aperture. If you look at my site (below) the imags of M83 and M16 were both taken this way. Also over 1000mm and you probably should be using OAG.

Peter
Peter I was actually hoping to use it mostly with my 8" newt. Would this still work? If I use a 2x powermate, I would get about 1600mm fl giving me something similar to a GSO 8" RC. Of course I could just buy one of those...

Quote:
Originally Posted by gregbradley View Post
Download the free ccd calculator by Ron Wodaski. Its very handy for seeing what the field of view will be with different telescope/camera combos including reducers, barlows etc.

The Tak 1.6Q extender is a nice piece of gear which I have used to image a galaxy with a TEC180 and KAF8300 chipped FLI Microline 8300.

It takes longer but does work.

Reducers can be tricky as they often give coma in the corners.

Greg.
Thanks Greg. I have been using the utility at this URL http://www.skyatnightmagazine.com/field-view-calculator
I think it's fairly good, and you also get a visual representation of what you may image when used as a package. Gees, I hope it's accurate anyway.
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Old 22-07-2014, 07:47 AM
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Sorry Goran,

I read your equipment list too fast and stopped after seeing the 80 mm refractor. It ought to work fine with an 8" reflector. Just be sure you have the proper focus travel. The barlow setting relative to the CCD is not as tricky as with a reducer. On the AP barlow that I use the power changes a bit but good images are returned over quite a range of distances. You might want to consider the AP barlow as it is pretty darn good and available. The one negative that I encountered is the lack of 2" filter threads on the scope end. I needed those threads for a light pollution filter and had to build a special camera adapter as a work around. I spoke to AP about this at the expo in Tucson last year and they said there will be a new model with threads. You might want to ask if you are thinking about this one. I cannot speak about the TAK extender. It's probably also quite good but you had best check on thread sizes etc as I understand TAK can be a bit "different" in that department.

http://www.astro-physics.com/index.h...acc/visual_acc

Peter
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Old 24-07-2014, 06:42 PM
kosh
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Quote:
Originally Posted by PRejto View Post
Sorry Goran,

I read your equipment list too fast and stopped after seeing the 80 mm refractor. It ought to work fine with an 8" reflector. Just be sure you have the proper focus travel. The barlow setting relative to the CCD is not as tricky as with a reducer. On the AP barlow that I use the power changes a bit but good images are returned over quite a range of distances. You might want to consider the AP barlow as it is pretty darn good and available. The one negative that I encountered is the lack of 2" filter threads on the scope end. I needed those threads for a light pollution filter and had to build a special camera adapter as a work around. I spoke to AP about this at the expo in Tucson last year and they said there will be a new model with threads. You might want to ask if you are thinking about this one. I cannot speak about the TAK extender. It's probably also quite good but you had best check on thread sizes etc as I understand TAK can be a bit "different" in that department.

http://www.astro-physics.com/index.h...acc/visual_acc

Peter
Thanks Peter,, I'll definitely look into this.
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Old 24-07-2014, 07:24 PM
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Hi Goran

I've recently gone through the same upgrade thought processes, and love to image galaxies. I've moved up from 600mm (ED80) at f/7.5 (with a DSLR) to 1600mm at f/8 (RC8) (with an Atik314L+). I've also got a fairly cheap Lightwave 0.6x reducer (Altair Astro), which shows no sign of coma at the corners of the small Atik chip (not too bad either on a DSLR chip)/ This reducer works well with my Atik314L+ on an ED80 and also on the RC8. It gives me fast f ratios (about f/4.5) at 360mm and 960mm and handy FOVs for nebulae with the small Atik chip.

I think a Powermate x 2 on an 8'' newt should work fine, I almost went for this option - it kind of gets you an RC8 anyway. Oversampling is about right at 1600mm with the Atik314. Of course, with a powermate x 2, your f ratio will drop from f/4 to f/8. Per pixel, you will have only one quarter of the light. However, you would gain about 6-7 times as much sensitivity on the Atik314 vs DSLR when doing hi-res luminosity subs (no Bayer filter, and bigger pixels).

Only nusiance factor at is getting the right spacers/filter wheel widths to match the required back-focus distance on a reducer.

Sam
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Old 25-07-2014, 12:18 PM
kosh
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Hi Sam,
thanks for the info, looks like the 314l+ is viable at lower focal lengths so long as I can keep that coma away.
Can I ask what size filters you are using with it? will 1.25" suffice or will the 2" be necessary? I would have thought the former with this relatively small chip.
Also, how do you find the GSO RC 8"? Have you had any difficulty collimating it or otherwise? I ask because there have been a couple of threads over the last year which had people struggling to set the GSO RC's up.

Goran.
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Old 25-07-2014, 12:55 PM
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ZeroID (Brent)
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Haven't quite got there yet but I've got the 'Barlow' idea with my scopes. I picked up a 2" 2 x Barlow which should give 1428 on the Lunt and 2500 on the Newt. I figured that with a 2" barlow I'd only be using the middle part of the lens so reducing the coma effect.
Ob is just coming back online after the damage rebuild so hopefully will be able to test the theory out soon.
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Old 25-07-2014, 06:29 PM
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Hi Goran

Yes, 1.25'' filters dwarf the titchy 314 chip. In fact, 1.25'' filters are quite big really, I've been happily using a 1.25 Ha in a mini filter holder to cover my Canon 450D sensor.

Yes, I read a lot of RC collimating problem threads and worried ! The RC8 was my first reflector and it really isn't very difficult. I found the Liveview methods (with Bahtinov mask) only useful for largish collimation errors. Next best was just looking down the barrel indoors and making adjustments so that everything possible is symetrical. In any case, this is good practce for working out which screw does what, and how quickly. The best method I've found is a basic Cheshire eyepiece. It's pretty straightforward to follow the AstroTech AT10RC collimation pdf and collimation seems to hold very well. I probably could get collimation "perfect" using lasers etc, and a lot more time, but I'm pretty sure that first seeing, then tracking/guiding are now my dominant sources of resolution loss, not collimation. If you do get the scope a long way out of collimation, you can get it back again pretty easily.

Sam
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Old 27-07-2014, 12:29 AM
kosh
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Quote:
Originally Posted by SamD View Post
Hi Goran

Yes, 1.25'' filters dwarf the titchy 314 chip. In fact, 1.25'' filters are quite big really, I've been happily using a 1.25 Ha in a mini filter holder to cover my Canon 450D sensor.

Yes, I read a lot of RC collimating problem threads and worried ! The RC8 was my first reflector and it really isn't very difficult. I found the Liveview methods (with Bahtinov mask) only useful for largish collimation errors. Next best was just looking down the barrel indoors and making adjustments so that everything possible is symetrical. In any case, this is good practce for working out which screw does what, and how quickly. The best method I've found is a basic Cheshire eyepiece. It's pretty straightforward to follow the AstroTech AT10RC collimation pdf and collimation seems to hold very well. I probably could get collimation "perfect" using lasers etc, and a lot more time, but I'm pretty sure that first seeing, then tracking/guiding are now my dominant sources of resolution loss, not collimation. If you do get the scope a long way out of collimation, you can get it back again pretty easily.

Sam
Well at least I save some money on the filters

I think I've made up my mind regarding the camera. I'll have to get it before I either add a long FL scope, or powermate because I can see that the 1000D at F8 - F10 may be an issue. Although my Ed80 @ 7.5 didn't do too badly with ngc253 last summer on a 450D. See, I've already almost reconsidered and I can't even complete a paragraph without changing my mind. I'm going mad!
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