Deep sky camera advice

[paulyz]

I mount DSLR on Heritage 150p. DSLR without lens, I printed T-mount for that. Focus I get by moving my tube (need to shorter tube about 3-5 cm) to get focus.

In youtube you can find video about mounting DSLR on 150pds 

[imakebeer]

12 hours ago, happy-kat said:

Yes that's it, unless eyepieces are parfocal you often need to adjust focus when changing them.

With a reflector designed for visual observation when a camera DSLR is used instead of an eyepiece there is not always enough focus travel distance available for the DSLR to reach focus (often the DSLR chip in inset in the body 44mm for a mirrored Canon) , focus travel runs out of inward movement. Outward focus movement can always be accommodated for by extension tubes where needed. Backfocus becomes a critical distance when a comma corrector or field flattener is used as these with the imaging device have critical placement range.

The PDS reflectors are designed for being usable with a DSLR as well as an eyepiece and has a shorter tube (effectively moving the mirror higher when compared to the P of same length/aperture) (amongst other changes). If an eyepiece is used conversely an extension tube 2 inch long might be used in the focuser before the eyepiece to reach focus.

With a refractor when observing a diagonal is used, if instead a camera is used then the diagonal is often swapped for a 2 inch long extension tube then the camera in order to reach focus.

Thanks @happy-kat , I think that's helped make it a little clearer 👍

Possibly I've misunderstood a little, but are you saying the behaviour is different between refractors and Newtonians? I'd have thought it's the same, just that the light in a Newt is folded???

With my current refractor, for visual observation with a diagonal  and 25mm eyepiece (and of course the diagonal has length, just with a mirror in the middle) I'm pretty sure I have to wind the focuser most of the way in to achieve focus.

Conversely, with a DSLR and the same 25mm eyepiece I have to wind the focuser most of the way out (maybe an extra 50mm) PLUS I'm using a telescopic eyepiece projection adapter (100mm or so) PLUS the distance from the T-ring to the DSLR sensor (30-40mm)...

It just surprises me there would be such a marked difference between visual and photographic... hmm... but I suppose the diagonal adds 50-100mm length, and the eyepiece is in a different position so maybe that has an effect too...

So many things to get my head around, but I like a challenge 😁

[imakebeer]

On 23/10/2022 at 14:35, paulyz said:

New and I think very useful video about old DSLR these days 

 

 

My setup ready, printed T mount, mounted camera on telescope, focused (big advantage of Heritage 150p that I can focus just sliding tube), connected to pc  did test shots and video. Sky cloudy (100% coverage ) all weekend so taked test photos of city. Result good, need to wait clear sky. 

That's a useful video @paulyz , thanks for sharing - I have the same model (450D / XSI) I picked up recently from eBay for not much. Much as a dedicated ZWO camera would be nice, that video suggests there's a lot to learn about process and you can still achieve a lot with older gear.