ASI071MC Pro with wide angle lenses

[CalvinKlein]

Has anybody here tried using an ASI071 MC-Pro with wide angle lenses - example 35mm F1.4 ? I'm considering buying one and would like to be able to use it for DSO and nightscape imaging.

I've tried my 14-24mm and 35mm EOS lenses with my ASI1600 and ASI183's with rather awful results (like stars in the middle being in focus but out of focus or severe aberations towards the outer edges).

I tried stopping down and adjusting the flange-to-sensor distance.

Given that the 071 sensor is apparently the same APS-C sensor used in some DSLRs I thought I might be able to use my wider lenses for doing nightscape work with it - up to 180 degree multi-row mosaics of the Milky Way with the ground.



Thanks, Kelvin.

[ChrisV]

Not that wide but I've started using it with a Rokinon 135mm. I use the zwo adaptor. It's okay to my untrained eye. A bit of star flaring on the edges but I probably haven't got the spacing quite right yet.

[CalvinKlein]

Thanks Chris - I figured the 135mm would be ok - I've seen plenty of people use it with the 071. I assume you are supporting the lens somehow and not relying on the weak flange of the ZWO adapter (I support the front of mine AND use a thin shim between adapter and lens to minimise the tilt)

[JA]

Whilst I haven't tried with the ASI071, I have used various wide lenses with various DSLR fullframe bodies for astro. In this use coma and astigmatism are often obvious abberations that you will have to contend with particularly at wider apertures. Certainly you will get the wider view that you want with the larger sensored ASI071, but you will also expose limitations in the optics as you start to use more of the image circle of the lens compared with using that same lens on the smaller sensors you mentioned: i.e: The likely abberations you were concerned with (probably coma and astigmatism) will get worse.



Correcting any error (if there is one) in the flange-to-sensor distance may improve the situation, but that's unlikely to be in error if you are using a one piece camera adapter. Maybe there is some load induced tilt, depending on lens support/play.

Stopping down will certainly improve the situation as the sensor sees less of the lens and its potential edge abberations, but the real improvement will probably unfortunately only be with a different lens, unless of course the Canon 35mm f/1.4 you have is the Canon EF 35mm f/1.4 USM LII which is EXCELLENT. The previous version, the Canon EF 35mm f/1.4 USM L suffers from very significant coma and astigmatism. See excerpt below prepared from lenstip.com comparing it with the new version II. The new version is quite expensive, but if you want to get most/all of the way there you could consider a significantly less expensive Sigma 35mm f/1.4 Art lens or Sigma 40mm f/1.4, also excellent.

Edit added:
You could also try a Samyang 14mm f/2.8 UMC for your 180 degree vista and you would only need 2 panels. It is very sharp edge to edge with very low coma. I haven't experienced it, but some complain of QC issues and sample variation with this lens. Another possibility if you are adventurous is the Nikon 14-24 f/2.8 which is also very well regarded and I've heard of Canon Astro shooters adapting it for their use on Canon bodies due to its sharpness and low coma.

Best
JA

[ChrisV]

Yes. Both camera and lens supported by nice big fat ADM rings bolted to a dovetail bar.

[CalvinKlein]

Thanks JA - good detailed information there which has got me thinking about the problem a bit deeper - especially the part about using more of the image circle and the inherent distortions the further out you go. By the way I use a Sigma 35mm F1.4 Art not the Canon.
I dont want to go too wide as star size and detail are affected. I've been doing some amazing Milky Way mosaics lately with my 6D and Samyang 135mm F2 but of course they take a long time to image and even longer to process and create the mosaic. But I want cooling (ideally set-point) and more Ha data. (theres a CentralDS modified & cooled 6D for sale in the IIS classifieds at the moment - that's why I'm looking at all this - versus for a similar price an 071MC Pro)

[Camelopardalis]

I’ve tried the Sigma 35mm f/1.4 Art with my ASI1600 and I was far from happy with the results. The 071 is a larger sensor, full frame much larger, than the 1600, so would only get worse.

Lenses that are great in daytime, or on paper, don’t necessarily translate to a good astro lens. Our objectives are more demanding, as we tend to pixel peep out to the corners.

[CalvinKlein]

Thanks Dunk - I guess I was hoping the opposite that the larger sensors would make it better but thinking logically that cant be the case..

Have you had any luck with other lenses on your 1600 ? I'd like to find something that rivals the Samyang 135mm F2 in quality - even if its around the 85mm mark. Macro lenses are supposed to be extremely good out towards the edges but very difficult to fine-focus at infinity.

[Camelopardalis]

Kelvin, lenses are usually designed to be sharpest at frame centre, and aberrations of some kind almost always creep in towards the edges/corners.

I’ve experimented with my 70-200mm with is more tolerant in some respects because it is the f/4 version.

The problem with “nice” lenses is they are heavy and this risks introducing tilt between the lens and sensor. I have yet to find an adapter I’m really happy with.

I’ve heard good things about the Samyang 135mm but never tried one myself.

[FrancoRodriguez]

Just wondering, what's your 70-200? Canon/Nikon/Sony? I've got the nikkor f4 version and an 071. Haven't tried them together yet (actually haven't tried any lens with it). What spacing did you use? Does it matter if it's off the recommended backfocus by 1 mm or so?
Thanks

[Camelopardalis]

My lens is the Canon 70-200 IS L for EF mount. DSLR lenses have substantially more backfocus for use with mono cameras than their mirrorless counterparts, which have smaller than half of the flange focal distance of DSLRs, typically.

I’d recommend hitting the backfocus spot on if you can - use thin metal/plastic rings to nail the right spacing as necessary. The lenses are designed to tight tolerances, so deviation from the ideal may result in undesirable aberrations that don’t show (or are minimised) at the intended backfocus. It’ll also throw out the focal point from the gauge on the lens.

Also, don’t forget that if you’re using a UV/IR cut (or any other filter) in front of the sensor, that will throw the focal plane further back. I think the figure is of the order of 1/3mm shift per filter thickness.

Hope that helps...

[CalvinKlein]

So I ended up buying the CentralDS 6D instead of the 071MC. The larger FoV and bigger pixels was very appealing and of course it will "just work" with all DSLR lenses. A guy I know who services Sigma lenses said that its common for lenses to be out of alignment in more than one plane, which can cause un-fixable aberrations unless the lens is sent for re-calibration.

[gregbradley]

William Optics has a new tight tolerance copper Canon T ring. I got one for my REdcat 51. Its quite heavy and the fit is very firm. It would minimise or get rid of any flex with your lenses.

Greg.

[Camelopardalis]

Thanks Greg, that T-ring looks really sweet :thumbsup:

Wonder if we could convince them to do the lens->M48 too?

[gregbradley]

Do you mean a male M48 end on the scope side and a Canon EF mount on the other? That's what this is.

Greg.