Imaging train with OAG and focal reducer

[Vox45]

Hi all,

Planning for my trip to the Alpes this summer. I would like to get some advices on a correct imaging train before buying anything.

So far I have done mostly lunar and planetary with a webcam. But as I will be in a good dark site I will try my luck at DSOs.

Right now I have a C6 on an HEQ5 mount and I will be using my Canon 1000D. I came up with a list of things to buy:

-> a Focal Reducer/Corrector to get to f/6.3

-> an OAG for guiding

-> a Crayford focuser

Now I am confused on how to set this all up. I read that the distance between the focal reducer and the chip should be around 105mm. That should not be an issue if I use a thin OAG like this one. But then, where do I put the focal reducer if I also add a focuser like this one .... does this even connect ?

Anyone with a similar setup that could avise on this ? Any recommendations on the individual pieces (quality wise) ? Eventually I will move to an ASI120MM and filter wheel ... I guess that will throw everything up !

Any chance of futur proofing this or am I cursed to resell everything and start anew ?

Ho the agony of buying new stuff !

[ecuador]

Eh, the only way I can think of for using such a focuser with your reducer would be to use a male SCT to 2" push fit adapter to put the reducer after the focuser. I mean the reducer has to keep a specific distance from the sensor, so that's not where the focusing is happening. I don't know if the distance from the secondary mirror will become too large to reach focus though, as you know you normally put the reducer directly on the back.

Also be aware that an f6.3 reducer with an APS-C sensor, especially on a C6 will give quite some vignetting. Of course you will need light frames.

[Vox45]

Also be aware that an f6.3 reducer with an APS-C sensor, especially on a C6 will give quite some vignetting. Of course you will need light frames.

I had found this 'MoonLite CS Model SCT Focusers' but it is quite expensive at 400€ but it does have the option to let you insert the Focal reducer in the focuser so it moves with the drawtube as you focus....

But now, you make me doubt. No one ever pointed that vignetting issue. Does this mean that I should avoid using a focal reducer ? This would make my C6 an f/10 imager... quite slow.

[ecuador]

Well, no, I didn't say that you should avoid it, but be prepared for the vignetting which you have to remove with flat frames. Without the reducer some people get away without flat frames.

I was disappointed myself because I tried it on my C8 which has a larger baffle tube than the C6 (38mm not much less than the reducer's 40mm) and did not expect significant vignetting, so I am giving the warning in case you also did not know. But what can you do, the DSLRs have big sensors with all that is good and bad

[Xplode]

In honestly think it's is a waste of money spending that much money on something that will never perform very good. Just the correct adapters to get it working will cost a lot.

The 0.63x reducer is Rubbish and flatteners/reducers for refractors will do a much better job...problem is that they are usually around 0.8x and the SCT will still be slow with a 0.8x reducer. A test was made that you can see here: http://stargazerslounge.com/topic/128928-sct-reducercorrector-test/

An 8" f/5 newtonian with a coma corrector won't cost much more and will give much better results at around the same focal length. 

It will be faster, less vignetting and much less frustration!

If you think the 8" is too large 6" would also be a good choice and very easy to handle. 

[Sp@ce_d]

I've got the Moonlite plus rotator/ internal reducer on my C925 adds a lot of weight & backfocus but it's a thing of beauty. I get rid of vignetting using flats but that's with a 314L no idea how bad it would be with larger sensor! I use the SX FW & OAG. I strapped a pair of ankle weights to the front of the tube but even then it's at the end of travel on the losmandy bar. The FR won't get you there any faster just give you a wider FOV really. It's a tricky one. I'd try not to spend too much on this. With no mirror locks the only way to keep good focus for me is automation with focusMax & constantly monitoring the fwhm values. DSLR s tend to sing with much faster scopes. I'm not trying to put you off trying but be careful how much you spend for the amount of effort to make it work for DSO use.

Sent from my iPhone using Tapatalk

[Vox45]

In honestly think it's is a waste of money spending that much money on something that will never perform very good. Just the correct adapters to get it working will cost a lot.

The 0.63x reducer is Rubbish and flatteners/reducers for refractors will do a much better job...problem is that they are usually around 0.8x and the SCT will still be slow with a 0.8x reducer. A test was made that you can see here: http://stargazerslounge.com/topic/128928-sct-reducercorrector-test/

I've got the Moonlite plus rotator/ internal reducer on my C925 adds a lot of weight & backfocus but it's a thing of beauty. I get rid of vignetting using flats but that's with a 314L no idea how bad it would be with larger sensor! I use the SX FW & OAG. I strapped a pair of ankle weights to the front of the tube but even then it's at the end of travel on the losmandy bar. The FR won't get you there any faster just give you a wider FOV really. It's a tricky one. I'd try not to spend too much on this. With no mirror locks the only way to keep good focus for me is automation with focusMax & constantly monitoring the fwhm values. DSLR s tend to sing with much faster scopes. I'm not trying to put you off trying but be careful how much you spend for the amount of effort to make it work for DSO use.

Sent from my iPhone using Tapatalk

I lost a bit of sleep over this. I think I am at a crossroads here. I got this setup really cheap from a friend (the mount/tripod/case/solar filter/motofocus/OTA for 375£) I feel that I could sell the OTA and accessories for a faire price, keep the mount and get a SW80ED.

I haven't spent money on any gear that only fits on SCT's yet (well, the bahtinov mask but it was only 15£) and I would hate to spend on a SCT focuser/focal reducer only to find out that I need a complete different setup.

As I don't do a lot of visual and my end game being DSO, an 80ED would make more sense from what I read on this forum. My concern is that I would still like to do solar/lunar and maybe some planetary and I may need to sacrifice planetary. My guess is that the 80ED on solar and lunar would do well... on planetary I am not sure ...

In the end I would have: 80ED+HEQ5+ASI120MM (guiding/planetary)+moonlite focuser+OAG+.8 focal reducer

Does this makes sens ? I read some people saying that I should keep the C6 for visual but I'm not really into that. Maybe one day when I have a big garden and house, I'll buy a big Dobson for visual

Any thoughts ?

[Xplode]

If you want to get good images with as little noise as possible with a DSLR the ED80 is no option either, you really want something as fast as f/5 so you overwhelm the noise with photons instead of the other way.  The ED80 is justy reduced to f/6.4 with it flattener/reducer.

Remember that a scope can't be great for both DSO and solar system imaging, i think you should keep the C6 for the solar system and get a fast scope for DSO.

[Vox45]

Remember that a scope can't be great for both DSO and solar system imaging, i think you should keep the C6 for the solar system and get a fast scope for DSO.

Yes that is where it hurts ... But perfectly understandable.

I would think that getting a MAK for planetary and a refractor for DSO would be a better option in my case ? The thing is that I cannot go down the 'big' scope road, I need to keep my gear small and a big newtonian is not something I would consider for now. As I am done with planetary (for now) I was thinking of selling the SCT to start in DSOs and save my money for a MAK when I'll get back to planetary next year...

[Xplode]

A refractor is a good choice, but they are expensive with faster f ratios, f/7 or faster with a 0.8x reducer would work great.

Could an 6" f/5 newtonian be an option or is that too large too? It's around 70cm length and easy to handle. Length is a little longer than the ED80

There's also the Skywatcher 130P-DS which is even smaller.

[Vox45]

A refractor is a good choice, but they are expensive with faster f ratios, f/7 or faster with a 0.8x reducer would work great.

Could an 6" f/5 newtonian be an option or is that too large too? It's around 70cm length and easy to handle. Length is a little longer than the ED80

There's also the Skywatcher 130P-DS which is even smaller.

I know I will sound like an heretic for some people but I don't feel at ease with a Newtonian... collimation, inward focus, the placement of the focuser itself (I like to sit down) Silly reasons and I know that I should not be put off by these things but I'd rather go with a refractor.

I am under the impression that the 80ED+HEQ5 is a good combination. I just put up my C6 for sale on eBay (just testing the water) It is a safe bet for me as it's costing me nothing (I may even make a profit) and if all fails I can always resell the 80ED.

I have to take the plunge or I'll never do anything

I will miss the planetary part though, but lunar and solar should be fine with the 80ED.

I'll dig for a suitable planetary scope later. Unless you have suggestions for that too ? I'd like to see what a MAK can do

[ecuador]

I think my planetary "shootout" with refractors, mak, newt, SCT would be of interest to you. Of course you will get better results with an ASI120mm, but you can see the relative differences.

I love the 80ED, and it can do surprisingly well for planets for its size. But note the "for its size", so complementing it with a larger aperture planetary scope is a good idea.

[Vox45]

I think my planetary "shootout" with refractors, mak, newt, SCT would be of interest to you. Of course you will get better results with an ASI120mm, but you can see the relative differences.

I love the 80ED, and it can do surprisingly well for planets for its size. But note the "for its size", so complementing it with a larger aperture planetary scope is a good idea.

I saw your 'shootout' a while ago and really enjoyed it ! Nice to see a side to side comparison. I have to say that the 80ED faired well (for my uneducated taste and to my surprise) on planets. Of course, nothing to compare with some of the pictures I see here sometimes with those C14... but then again, they usually are captured on good cams, not cheap webcam like mine

That being said, that is my next move: getting an ASI120MM. This is what got me into rethinking my setup... and not wanting to spend money on pricey elements and not get the most of it with a C6. The end game is to use the ASI as a guide camera for DSO's with a DSLR and a planetary cam (on a MAK eventually)

A day will come when I'll get further down the road and get an ATIK cam to replace the DSLR

I wish I could go for the 'best' setup possible but I do have constraint (space wise, money wise and experience wise) so my choice may make some people cringe, but I hope I have tought this through enough so I will not regret it...

But hey, you must learn to crawl before you can learn to walk....

[Tinker1947]

You should work out the distances required from the Flattener, OAG, DSLR Sensor, they don't just fit together there a finicky lot of bits to get together.....

[Vox45]

A refractor is a good choice, but they are expensive with faster f ratios, f/7 or faster with a 0.8x reducer would work great.

Could an 6" f/5 newtonian be an option or is that too large too? It's around 70cm length and easy to handle. Length is a little longer than the ED80

There's also the Skywatcher 130P-DS which is even smaller.

I finished reading another thread on 'going to straight to CCD' and I see that you recommended me to get a Skywatcher Esprit ED80 APO. It's a bit much at 849£ but it does look good ! Triplet and f/5 without a focal reducer

ho well ... not for now but at least I know what to aim for

[Vox45]

You should work out the distances required from the Flattener, OAG, DSLR Sensor, they don't just fit together there a finicky lot of bits to get together.....

Yes, that is another issue ... always a pain to sort out ... spacer and whatnot.

Thanks for pointing that out

[Xplode]

The Esprit ED80 is a very good choice and gives you the ability to produce good images

Note that with it's short focal length many targets will be very small in the late season...early season there will be some nice areas with Ha that is great at that focal length with a modified camera.

[ecuador]

I finished reading another thread on 'going to straight to CCD' and I see that you recommended me to get a Skywatcher Esprit ED80 APO. It's a bit much at 849£ but it does look good ! Triplet and f/5 without a focal reducer

ho well ... not for now but at least I know what to aim for

With a CCD that esprit will make a difference from the 80ED. With a DSLR it is probably worse, since you start to have a bit wider field than you would want for most targets (and you will also need a field flattener to get the best out of it - more cost!).