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Flattener spacing

blinky

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blinky

blinky

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Gus,

Has anybody any tips/tricks for getting the ccd to flattener spacing correct?  I have been trying for the past few nights to get the spacing correct with my ZS70 and Altair 1x flattener with little joy!  I initially started at 55mm spacing but have now increased it by a couple of mm and cant really see things improving, I suppose my major question is whats most likely, I need to reduce the space to less than 55mm or increase it over 55mm? Also, what should the max spacing be? I mean should I keep trying till I have something like 60mm or 50mm spacing or really should I only be adjusting it by a couple of mm either way?

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swag72

swag72

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I've always found the quoted spacing requirements quite precise when I've used a flattener / reducer. Make sure that you are measuring from the right place would be my advice. It seems there is little or no standard with this. Some measure from where it screws in, some from another point - I'd use that as a starting point - Making sure I am measuring from the right place, then get the spacing right from there.

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steppenwolf

steppenwolf

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This issue causes more difficulties for imagers than just about any other technical issue! To have a deep sky imaging 'industry standard' based on the confines of an unguided DSLR camera is quite ridiculous but for now, that's what we have!

I'm with Sarah on this, the figure supplied by the manufacturer is normally spot on and applies to the use of a DSLR camera with a nominal sensor to front mounting face measurement of 45mm (Canon are less at 44mm others are more) plus 10mm for the 'T' thread adaptor. This figure is normally 55mm plus or minus 1mm but that + or - difference can be significant.

If you are using a CCD camera, you must accurately ascertain the distance from the front of the sensor to the front mounting face of the camera - this varies widely from manufacturer to manufacturer (Atik mainly 13.mm, Starlight Xpress 17.5mm for example). Spacers then need to be added to make this the nominal 55mm. You need to be careful here though as the sensor position is not always perfectly accurate.

If your CCD camera is a mono version and you are using filters, you need to factor in the increased path length which varies with filter thickness  - Baader filters add 0.7mm to the spacing requirement making it 55.7mm.

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blinky

blinky

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Hmm..... Well I'm using a QHY8 CCD which has 6.5mm to the glass of the sensor, there is an IR filter in the way, I dont know how much that adds but I originally had it at 55mm, or so I thought..... I will get it back inside and have another look. One other problem I'm having is the ZS70 has a rotatable focuser and this is also not square, I noticed last night if I loosen the lock screw it does wiggle about a bit so I also need to look at that! To be honest Im only going to have another couple of goes with it then give up and save up for a Telescope Services 65mm quad! 

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Alien 13

Alien 13

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The WO scopes are normally very fussy with regard to spacing due the fast F ratio however the quoted figure is close mine is now at 56.2mm and the .2 does make a difference.

What might be happening is that the correction with a small sensor is very subtle i.e most of it is outside of the sensors image circle i think with my scope about 60% of the FOV is fine even without the FF.

Alan

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Alien 13

Alien 13

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If the star shapes are like lines running away from the center then the spacing is too close if however the shapes are radiating parallel to the center then the spacing is too great.

This is some info i saved from a post regarding FF spacing i cant remember who was the original poster but a big thanks to them.

Alan

Star shapes.docx

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Owmuchonomy

Owmuchonomy

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Yeah, on looking again it appears the top left and right and too far away and the bottom left and right are OK - will need to have another look at the focuser, I think it's that, thats the source of the problem now.

I will follow your exploits as I have the same issue with the same flattener but using a DSLR. I am exchanging photos with the distributor.

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Owmuchonomy

Owmuchonomy

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I am travelling this week so I can't send photos. I went through the retailer. They sent me a replacement flattener which is very similar I'm afraid. I'm not ruling out spacing but that's not the point in my view. It is supposed to work with a generous tolerance of +\- 5mm. I have 2 DSLRs and they both test similarly.

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steppenwolf

steppenwolf

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If the star shapes are like lines running away from the center then the spacing is too close if however the shapes are radiating parallel to the center then the spacing is too great.

I have heard of this before (same source) but never experienced it. Has anyone on SGL actually seen this effect for themselves rather than read about it? Please don't get me wrong, I am not suggesting that the information is incorrect but it is surprising that there seems to be little published about what would, on the face of it, appear to be such a good indicator of what adjustment needs to be done!!

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Alien 13

Alien 13

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I have heard of this before (same source) but never experienced it. Has anyone on SGL actually seen this effect for themselves rather than read about it? Please don't get me wrong, I am not suggesting that the information is incorrect but it is surprising that there seems to be little published about what would, on the face of it, appear to be such a good indicator of what adjustment needs to be done!!

I have certainly seen the effect as described when the spacing was too close and used the info to add more but did not push it the other way.

Alan

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Owmuchonomy

Owmuchonomy

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Ah..... This is interesting, so it might be the flattener itself? Can you send me one of your photos to compare? I might do the same as you, call the distributer

Sent from my iPad using Tapatalk

I'm sure it wouldn't do any harm to contact them with your photos. It may help them formulate a possible solution.
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steppenwolf

steppenwolf

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I have certainly seen the effect as described when the spacing was too close and used the info to add more but did not push it the other way.

Alan

Thanks, Alan - it's the 'radiating parallel' that I haven't seen yet  - I really should test this out!

Apologies for small hijack, Blinky.

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Owmuchonomy

Owmuchonomy

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Ah..... This is interesting, so it might be the flattener itself? Can you send me one of your photos to compare? I might do the same as you, call the distributer

Sent from my iPad using Tapatalk

How are you getting on with this? Have you heard from Altair?
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blinky

blinky

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I rotated the focuser by 90 degrees and it seemed to sort it a lot, now the spacing is still slightly out but it seems to be the same in all corners. So I think I just have to tweak it a little

Sent from my iPad using Tapatalk

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ian_bird

ian_bird

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Hi

I was the person who posted the "too close" "too far" pictures. They came from Teleskop Service - and they work for me. I have seen both effects.

Too Close.

post-26501-0-55232800-1412182871.jpg

Too Far.

post-26501-0-76907500-1412182914.jpg

It really does work! Honest. Well - it worked for my Riccardi Reducer/Flattener on my WO98.

Cheers

Ian

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