I think I'm nearing a decision: Does this setup sound good?

[pipnina]

Having talked with the people at FLO a little as well as you guys, I think I have a final idea of my likely imaging setup:

• Explorer 130-PDS
• HEQ5-PRO
• And the Explore Scientific HR coma corrector

Does this sound like a good starting point? I hear the HEQ5 and the 130PDS used and used here a fair bit.

My only worry is potential over-spending on the coma corrector... But it tempts me with the adjustable distance (having talked with @vlaiv the ideal spacing for other coma correctors would be 55mm, and since my camera + T2 + adapter comes to something like 48 I would need adapters and such otherwise, which sounds a bit annoying).

What do you guys think? Should I summon more clouds now or sit on this for a while longer?

Cheers

[alacant]

26 minutes ago, pipnina said:

other coma correctors would be 55mm

The HR is also needs 55mm to the camera sensor.

27 minutes ago, pipnina said:

my camera + T2 + adapter comes to something like 48

Really? Even if it is, you would simply need 7mm extension ring; far more economical than the HR!

The other thing to consider is the HR focus position which is around 4cm further out than normal. The idea of the sw focuser -if it even gets that far- that far out scares me. Maybe you could ask FLO to set it up and send you a snap so you could see for yourself.

IMHO, if you're gonna spend that much for a flat field, go for the GPU. OTOH, if you're gonna do visual, the variable HR is a godsend.

HTH and clear skies.

[vlaiv]

Specs for ES HR CC (a lot of capital doublets? ) say that for photographic use you still have 55 spacing requirement, according to TS website, here is link:

https://www.teleskop-express.de/shop/product_info.php/info/p8688_ES-2--HR-Coma-Corrector-for-photography-and-observing.html

Look under Technical data tab. Description also states:

" The corrector is delivered with photographic adapters (T2 and M48x0,75). Theys are screwed on instead of of the helical fokuser. The working distance is standard - 55 mm from the thread for easy adaption of CCD and DSLR cameras. " (sic)

I would say that this CC is a sound option if you are going to use it both visually and photographically. Otherwise I don't see any particular advantage over some less expensive models that also operate on 55mm distance - like Baader MPCC MK III for example? I don't know how each of them fares optically.

[pipnina]

8 minutes ago, alacant said:

The HR is also needs 55mm to the camera sensor.

Really? Even if it is, you would simply need 7mm extension ring; far more economical than the HR!

The other thing to consider is the HR focus position which is around 4cm further out than normal. The idea of the sw focuser -if it even gets that far- that far out scares me. Maybe you could ask FLO to set it up and send you a snap so you could see for yourself.

IMHO, if you're gonna spend that much for a flat field, go for the GPU. OTOH, if you're gonna do visual, the variable HR is a godsend.

HTH and clear skies.

 

7 minutes ago, vlaiv said:

Specs for ES HR CC (a lot of capital doublets? ) say that for photographic use you still have 55 spacing requirement, according to TS website, here is link:

https://www.teleskop-express.de/shop/product_info.php/info/p8688_ES-2--HR-Coma-Corrector-for-photography-and-observing.html

Look under Technical data tab. Description also states:

" The corrector is delivered with photographic adapters (T2 and M48x0,75). Theys are screwed on instead of of the helical fokuser. The working distance is standard - 55 mm from the thread for easy adaption of CCD and DSLR cameras. " (sic)

I would say that this CC is a sound option if you are going to use it both visually and photographically. Otherwise I don't see any particular advantage over some less expensive models that also operate on 55mm distance - like Baader MPCC MK III for example? I don't know how each of them fares optically.

Re-checking on google, it seems my camera's flange distance is 46.5mm, measuring my T2+adapter's combined focuser extension seems to be just shy of 10mm. This could land the total distance at around 56 or 56.5mm. Would that be an acceptable margin? If then I go for a cheaper CC like the MK3 it would be approx £100 cheaper and i might not need any further adapters?

Having re-measured it (although I'm using a tape measure - the micrometer is in the garage somewhere - only dad knows where) it seems closer to the 10mm mark than the 9.5mm mark.

[vlaiv]

What type of Nikon F - T2 adapter do you have?

It looks like Baader adapter has optical path to give you exactly 55mm so you would not need any spacers if you have that one.

GPU CC indeed seems to be better option (more expensive) than Baader MPCC III - I've seen reports that Baader has bloated stars at F/4 scopes - you will be using F/5 scope so it might not be an issue. Problem with GPU CC is that optimum distance is even less than 55mm in your case - 130pds

here is table of distances:

F=600mm, working distance = 51.66mm
F=800mm, working distance = 53.66mm
F=1000mm, working distance = 55.0mm
F=1200mm, working distance = 54.66mm
> 1500mm, working distance = 54.60mm

So I guess 52mm would be good distance for GPU CC.

 

[alacant]

16 minutes ago, vlaiv said:

52mm would be good distance for GPU

Hi. The GPU is m48. Your best chance is this + a 5mm m42 to m48 adaptor. Or just screw it directly into one of these. It doesn't seem too fussed by the spacing.

Perhaps even better, just get the cc that sw designed which has the advantage of giving a nice wide field of view.

HTH.

[pipnina]

30 minutes ago, vlaiv said:

What type of Nikon F - T2 adapter do you have?

It looks like Baader adapter has optical path to give you exactly 55mm so you would not need any spacers if you have that one.

GPU CC indeed seems to be better option (more expensive) than Baader MPCC III - I've seen reports that Baader has bloated stars at F/4 scopes - you will be using F/5 scope so it might not be an issue. Problem with GPU CC is that optimum distance is even less than 55mm in your case - 130pds

here is table of distances:

F=600mm, working distance = 51.66mm
F=800mm, working distance = 53.66mm
F=1000mm, working distance = 55.0mm
F=1200mm, working distance = 54.66mm
> 1500mm, working distance = 54.60mm

So I guess 52mm would be good distance for GPU CC.

 

This is the one I'm using https://www.firstlightoptics.com/adapters/t-rings.html

If my combined minimum distance from focuser to CC is 56mm, would a 52mm spacing not under-correct?

Might it be better to use the slightly cheaper skywatcher 0.9x for this scope if I can't shave a few mm off the spacing with a different T ring?

[vlaiv]

I'm not sure that combined distance is 56mm - according to Baader - and they have very similar item (Nikon F - T2) - it has optical path such that spacing is proper 55mm. Maybe sending an inquiry to FLO would resolve this? Just ask them of optical path for that particular item - what is total distance.

here is link to baader T2 adapter

https://www.baader-planetarium.com/en/accessories/adapters-imaging-accessories/camera-adapters/classic-t-rings/baader-t-ring-nikon-to-t-2.html

" Represents the standard exact distance of 55.0mm from the front support surface of the T-ring to the image plane of the camera body forth "

I've been talking to @Uranium235 recently and has mentioned that SW CC produces internal reflections he did not like - he also mentioned that he would probably go for MPCC III with 130PDS. Maybe he can shed some light on that.

[Uranium235]

Yeah, the MkIII is a good corrector, its t-thread and collar is also removeable to it leaves you with an M48 cell (spacing distance from M48 is 57.5mm). The spacing can be variable to some degree, it depends on what size sensor you are trying to cover, and how many filters are in the imaging train.

[pipnina]

5 minutes ago, vlaiv said:

I'm not sure that combined distance is 56mm - according to Baader - and they have very similar item (Nikon F - T2) - it has optical path such that spacing is proper 55mm. Maybe sending an inquiry to FLO would resolve this? Just ask them of optical path for that particular item - what is total distance.

8 hours ago, Uranium235 said:

Yeah, the MkIII is a good corrector, its t-thread and collar is also removeable to it leaves you with an M48 cell (spacing distance from M48 is 57.5mm). The spacing can be variable to some degree, it depends on what size sensor you are trying to cover, and how many filters are in the imaging train.

I measured the T2 adapter by itself (without the bottom half of the 2"-1.25" adapter) and it measures closer to 8mm (meaning the 2"-1.25" must be adding close to 2mm) which would make the distance about 44.5. So I might be a little bit out either way.

I don't imagine I'll be using any filters for the time being. I use my D3200 for regular photography so IR mod and debayering can't be done. CCDs are basically their own price range above what I'd be spending on this whole scope/mount setup so that will have to wait until another season.

Thanks for your help guys

[alacant]

11 hours ago, pipnina said:

go for a cheaper CC

Hi. You don't need to correct the coma in hardware. Lose the cc and correct in software. E.g. StarTools' lens module does a fine job and as it doesn't involve light passing through glass, introduces no further aberration of its own.

To connect to the telescope you need one of these instead of the cc. HTH.

[michael.h.f.wilkinson]

50 minutes ago, alacant said:

Hi. You don't need to correct the coma in hardware. Lose the cc and correct in software. E.g. StarTools' lens module does a fine job and as it doesn't involve light passing through glass, introduces no further aberration of its own.

To connect to the telescope you need one of these instead of the cc. HTH.

Correction in software is effectively a non-uniform deconvolution problem, and given that all deconvolution problems are ill-posed mathematically, they can introduce noise. I would certainly go for a (quality) optical solution