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I'm trying to help a friend out with a problem in getting filters between his new ZWO ASI-2600MC DUO camera with it's 17.5mm back focal distance and his RASA 8 corrector lens assembly. The total working distance here is 28.73mm (according to Celestron) so with the 17.5mm back focus taken off gives 11.23mm. Fortunately a 2mm filter thickness is required when using the RASA 8 so no additional spacings are needed (just need to remove the factory fitted one).

Originally I was going to machine an adapter from a solid aluminium disc but the RASA 8 comes with a 'C-mount' which just happens to be the correct depth once the 'c-mount' is removed, meaning I don't have to machine the radial slots for the RASA collimation adjusters.

The ASI2600MC DUO has an M54 female front thread to accept any attachments. So I needed to put a 55mm minimum central hole in the RASA's C-mount plate to give a clearance to the new insert's 54mm thread.

A piece of ali rod was then turned to match the internal dimension of the C-mount and it's centre bored out to 45mm in prep for cutting the 48mm filter thread later. The outside was the turned down to 55mm over an 8mm distance to be a snug fit for the hole in the C-mount plate.

The outward 5mm was then threaded to 54mm x 0.75mm pitch to match the threaded face of the camera. This would take the threaded section below the approx 4mm thickness of the C-mount RASA adapter plate to prevent any thread fouling.

The ali rod was then parted off with a small excess. The 45mm threaded section was inserted through the C-mount adapter plate and a 54mm extension tube used to lock the insert in place inside the C-mount plate.

The extension tube could then be placed in the lathe and the inner face of the insert cleaned up to size and the 48mm x0.75mm internal thread for the filters cut. The 5th image has a schematic inserted giving a cross section (not to scale) of the insert.

Internal view - Filter in place

Internal view - Filter removed

External view showing the 54mm male thread to fit the camera and the filter thread

Internal parts view

External parts view - Cross section (not to scale) to give an idea of the insert shape.

The adapter mounted on an ASI 2600MC DUO to show clearance to guide sensor

Keith,

Been looking at the RASA white paper and the Duo my thoughts are you would need an adapter plate with this type of profile having a 50mm central aperture, with a 54mm male thread to fit the Duo with a thickness to give the required 28.73mm from the back face of the adapter plate to the sensor plane. Should be able to do that but don't have the ali at the mo. Might  build quite a thrist doing this!

If you can mount your camera onto the standard RASA adapter (42mm) with a step up ring 42/54mm then mark where the guide camera focuser knob is on the RASA mount and drill a suitable sized hole in the RASA mounting plate to allow light through to the guide camera... May need some back focus adjustment for the main camera to meet the 25mm RASA spec's.

just a thought...

1 hour ago, Elp said:

Looks good. No issues with finding suitable guidestars? I'm curious how this would work at 1000mm+ FL using something like an lextreme.

I'll be trying it with an IDAS NBZ and Askar 6nm duo band (Ha/OIII) in the near future but I want to get the final tweaks in PHD2 and iOptron's Commander sorted out, especially PHD2 which was a real PITA last night before I switched to NINA. Even then some subs were not guided as it kept timing out and not settling after a dither. Yet it's graph had spiked with the dither and resettled and was chugging away skimming the centre line?

Like most things new there were a few trials before things smoothed out slightly and I got a couple of images to show for what felt like .....   Well most of my problem were a cable (USB 3) which needed swapping but I think settings in PHD2 was my biggest headache.

Finally I got two sets of subs: 15x 60s on the Wall in NGC7000  and 14x 60s of NGC6995 these were captured through my Orion Optic (UK) VX10 with a TS GPU 1x super flat coma corrector (55mm back focus) The two extn tubes and the 17.5mm backfocus of the Duo were 55mm. No filters were used for these images.

Processing was via PI without the use of the RC-Astro routines as I wanted to see what the camera, corrector and telescope produced without the intervention of AI.

With RC-Astro:

If you can carry your kit in still assembled then I've found that I've marked my patio where the three tripod legs sit before moving stuff indoors. Then next day I drilled three holes at the marked positions and now I can place the tripod legs in the holes each time and very little adjustment is needed. I do extend tripod sections but to their stops so constant each time. Mark one leg and its hole so you put the same leg in the same hole each time...

Brilliant execution Peter, just jealous of all that exposure data…

Wow! Incredible. To me whats striking is the amount of dark dusty stuff thats showing. Magicians all involved...

9 hours ago, peter shah said:

Thank you Francis...the seeing has been good recently really helping this image

I take it we’re not talking Powys UK! Because Hereford hasn’t seen sky for ages…

Another superb piece of work Peter. Spanish skies strike again.

A simple statement like I'm a visual astronomer or I'm an imager which is my best option...

Superb Peter as ever.

10 minutes ago, Ratlet said:

I've found a 130pds works well on an azgti, so the heritage 130p will work well.  I think it's the shorter focal length reduces the movement arm.

I have found though that the tripod makes a huge difference in stability, I'd it's the cheap aluminium tripod I'd consider upgrading it to the 1.75" steel tripod.  Makes a huge difference in stability although it is much bigger and heavier than the aluminium

I use a surveyors tripod much much cheaper than an astro tripod. just change the anchor bolt to 3/8th UNC or Whit thread.  https://smithsurveyingequipment.co.uk/product-category/surveying-accessories/tripods/

No affiliation etc... just bought a tripod.

Many thanks

Is that an Orion UK carbon tube upgrade or from somewhere else?

I have a VX10 and am thinking longer term about a carbon tube upgrade....

Currently - My Orion Optics (UK): VX10 on an iOptron CEM60 in my little Obsy.

Tackle your back focus spacing first to remove the field curvature then see what if any tilt remains because 4/100ths of a degree tilt showing isn't much.

Needs to be as close to the camera sensor as possible. Your heater is doing nothing but warming the outside air so entrapping it behind a tilt plate might make your heater more efficient.

Are you sure you need a tilt plate. Your using a refractor, what appears to be a matching reducer flattener - try small changes to your back spacing. Or even try placing a slip of paper in different positions around the spacer/camera to give a little 'tilt' and see if you detect a change. (Single thickness of printer paper is thick enough about 20mm wide).

It might be you heater that's not an even thickness. Try removing that and see if the error remains...

Sorry lots of suggestions but your basic kit looks outwardly sound.

Superb Dave, yet again.

42 minutes ago, Anthonyexmouth said:

Ah, the cooling test in the review didn't really criticise the QHY, just happened to say the ZWO was able to get a little further below ambient than the QHY. 

What temp do you usually run the 26c at?

Usually -10 although with these warm nights -5 is enough.

Re: Cooling. My AA 26C has kept very well to temperature even during this hot spell ± 0.1C with a pull down of circa  -20°C below ambient and the 0.1°C was only ever momentary

54 minutes ago, Anthonyexmouth said:

Has anyone seen a good comparison for these 2 cameras? I've seen a few comparing the ASI to QHY but none directly comparing the ZWO to AA. On the face of it it's hard to justify the additional £600+ for the ZWO. Anyone know a good reason to spend the extra? 

I bought the AA 26C in Jan this year and its a great camera. Currently selling only because I'm after a duo chip'd 2600MC.

8 minutes ago, pipnina said:

You can buy 5x4 and larger sheets from various companies including kodak and Fujifilm as well

Velvia 100 is available in 5x4 but you will be paying like 140 quid for a 20 sheet box! Then you have to pay for development...

Probably stick with B&W then process negs and scan at home before printing/viewing.

6 minutes ago, Mandy D said:

Ilford still make and sell film. They also provide a special service once a year where they make what you want in large format sheet form, etc.

That's interesting. I have a 5x4 format aerial camera lens that I set-up years ago to do night sky work with but it's never really been used...

@scotty38 Thanks, Same settings so I'll try again and deactivate the stop tracking when done and see what happens...

Really good to be able to get PA with no view of the pole.