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ASI183 new camera - spacing...

Ant

By Ant
in Discussions - Cameras

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Ant

Ant

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Over the last few weeks i've managed to get myself a new ASI183mm pro, ASI120MM guide camera, ZWO OAG and Filterwheel.

Also an ED80 with steel track focuser and FF/FR.

This zwo kit is incredible, it looks really nice, lovely build quality and a whole host of adapters, spacers, leads, tools, extension tubes... the list goes on.

The last batch of bits arrived today so i've been putting it all together. How pretty does this all look :)

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 I have a question on spacing. I'm pretty sure that the FF/FR has to be 55mm from the camera. Now I assume that this is the back edge of the FR to the chip - is that right?

Where would be the best place to place the extension? Between the Filterwheel and OAG, or between OAG and FF/FR? 

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Cheers

Ant

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alexbb

alexbb

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In your case with that extender between the OAG and the guide camera, it could go between the OAG and the 183. Mine's a bit different, I don't have anything between the OAG and guide cam so I put an extension between the ff and the OAG.

And yes, 55mm from the fr/ff back end to the sensor.

Looking forward to see some nice pictures.

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Ant

Ant

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Because of the chip size, its suitable for 1.25" filters (just), I've been told that the FW needs to be as close the the camera as possible.

So I guess between  the FW and OAG would be a good start and  see what happens.

Thanks for the 55mm confirmation :)

Ant 

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Lonestar70

Lonestar70

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2 hours ago, Ant said:

Because of the chip size, its suitable for 1.25" filters (just), I've been told that the FW needs to be as close the the camera as possible.

So I guess between  the FW and OAG would be a good start and  see what happens.

Thanks for the 55mm confirmation :)

Ant 

Hi Ant,

The 55 mm distance is correct from the FF flange face to the sensor, however, you will also need to add a correction for the filters being used.

This is generally taken to be 1/3rd of the filter thickness and should be added to the 55mm back focus distance.

Good luck and clear skies.

 

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Ant

Ant

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Haha thanks. 

1/3 of the filter thickness? How think are they likely to be? Not that I've bought any yet. 

Going to be fairly important to buy matching NB filters then. I might even buy a 2" LP filter so that can go in front of the FR/FF. I cannot be doing with trying to adjust the distance by a fraction if a mm in the middle of the night :)

How precise does it need to be?

Cheers

Ant

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Lonestar70

Lonestar70

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I will agree to differ on that...

The document you linked clearly states that the filter reduces the back focus by between 0.33m and 1.0mm depending on filter brand. (Back focus reduced by glass thickness / 3)

However, this reduction applies only to the optical path of the camera/filter wheel assembly... it does not change the back focus requirement of the FF which will remain at 55mm, therefore you would need to add an extra spacer of the same thickness as the above reduction between the FF and the filter wheel assembly to bring it to the 55mm required between the FF and the camera sensor.

There may also be an additional +/- adjustment needed for the specific camera sensor height.

It can all get a little confusing.

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DaveS

DaveS

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Baader are 2mm thick, Astrodons (Yeah, Right!) are 3mm, Astronomik (Which auntie Flo does now) are 1mm, so will barely need correcting, they are parfocal with their NB filters too. Not sure about ZWO.

Myself, if buying now, I'd probably go all Astronomik if on a budget, all Astrodon if flush.

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IanL

IanL

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12 hours ago, Ant said:

Haha thanks. 

1/3 of the filter thickness? How think are they likely to be? Not that I've bought any yet. 

Going to be fairly important to buy matching NB filters then. I might even buy a 2" LP filter so that can go in front of the FR/FF. I cannot be doing with trying to adjust the distance by a fraction if a mm in the middle of the night :)

How precise does it need to be?

Cheers

Ant

I had a 2" IDAS that I used with my DSLR and 0.85X reducer. When I moved over to an ASI1600 with a filter wheel I tried it in front of the 0.85x reducer but could not make it work. Everything was fine without it but impossible to get focus with it (I think the extra glass was creating multi-order reflections that looked like bad focus to be honest).

You won't need it for narrowband anyway but might be more useful to put the money towards higher quality filters.

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steppenwolf

steppenwolf

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I'd put the spacer between the OAG and the FF/FR so that the prism is further down the 'light cone' towards the camera.

At the risk of all out war (again!) :unsure: the filter diffraction refraction means that you need to increase the mechanical spacing between the mounting face of the FF/FR and the sensor by approx 1/3rd of your filter thickness.

P.S. the new outfit looks great!

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Lonestar70

Lonestar70

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20 minutes ago, steppenwolf said:

I'd put the spacer between the OAG and the FF/FR so that the prism is further down the 'light cone' towards the camera.

At the risk of all out war (again!) :unsure: the filter diffraction means that you need to increase the mechanical spacing between the mounting face of the FF/FR and the sensor by approx 1/3rd of your filter thickness.

P.S. the new outfit looks great!

Thanks Steve for your input on this issue, it confirms my reasoning of the correct spacing requirement.

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Ant

Ant

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Thanks guys, I've done my measuring. I think i need a 10mm extension.

Before i rush out and buy, need to check all the boxes that the kit came in. There were a load of adapters/extensions.

So im getting close :)

First light may even be without the correct spacing, it cannot be any worse than no FF/FR at all. If nothing else it'll let me focus both the main and guide cameras :)

Ant

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Yawning Angel

Yawning Angel

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Hi Ant. I'm building basically the same setup, but with the 1600mm pro. My intended spacing, goes like this:

Field Flattener -> OAG (16.5mm) -> 13mm spacer -> EFW (20mm) -> Camera (6.5mm minus filter allowance (1.9mm / 3 = 0.63mm) = 55.37

The 1.9mm come from the ZWO filter thickness spec

Looking at the drawings, the asi183 is the same size, in terms of it's back focus, plus it also comes with the same 11mm T2 ring attached. I've used the knurled T2 to T2 (2mm) to make up the 13mm spacer - all assuming my maths is correct

Hope this helps...or someone points out where I've gone adrift :icon_biggrin:

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Ant

Ant

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Thanks Alex, you made me go and check the drawings again. 

Yeah, your right. The back focus is 6.5mm NOT 8.6 - so my calculations are all wrong. Maybe your's will work for me. 

If I get a chance today I'll pop back out into the garage and do another measuring session :)  See if I have that adaptor you mention.

Cheers

Ant

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Ant

Ant

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I do indeed have the adaptor(s) of which you talk. 

I'll get that into the imaging train tonight, and that will be what I work with untill I buy filters... So it'll be a 2/3mm out for a little while.

Ant 

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Yawning Angel

Yawning Angel

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That's great! Without a filter in the path, I think you'd need 12mm, so you could use the 11mm T2 from the camera nose and the 2 flexible shim ring to get you to 11.7 (16.5+11.7+20+6.5 = 54.7mm total) alternatively you'd be at 16.5+13+20+6.5 = 56mm

Under by 0.3mm or over by 1mm - I have no idea which is best, whilst you wait on filters

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Ant

Ant

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Trouble is the 11mm is female both sides. So you need the 2mm Male/Male to be able to get it into the imaging train. I have a load of Delrin spacers so can easily use those to increase the spacing by a few mm if I was so inclined. 

To be honest my imaging isn't going to be great till I get a filter (either LPR or NB). So I can practise till then, being a mm out with the FF/FR cannot be worse than not including the FF/FR!!!  :D

Cheers

Ant 

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Ant

Ant

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31 minutes ago, Yawning Angel said:

Gah, of course!

I'm waiting on the (out of stock) Ha filter so I can fully populate the wheel before building it up, as the 2mm spacer covers the top 2 screws on the EFW.

Always the way :)

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