Throwing Good Money After Bad?

[Ian McCallum]

Having the Sky-Watcher Startravel 120 achromatic refractor on a EQ5 Pro SynScan mount, I've dabbled in a bit of astrophotography. This has been mainly with a ZWO ASI 224MC planetary camera, but I'd like to get something with a larger sensor. 

I was thinking of the ZWO ASI 533MC uncooked version, due to my budget. I know the limitations of the telescope due to CA, but do you think I'm throwing good money after bad? 

[scitmon]

By uncooked do you mean the non cooled one?  If so I would rethink that, save a little longer for the pro version, or shop around for a second hand one.

As for CA on the Startravel... not sure on broadband images, but if you go down the narrowband route you can certainly get decent results.  Example: https://www.astrobin.com/dlrjp8/0/ 

I think the big question mark is your mount, have you experimented already on how long an exposure you can get before star trailing starts?  

 

[Ian McCallum]

25 minutes ago, scitmon said:

By uncooked do you mean the non cooled one?  If so I would rethink that, save a little longer for the pro version, or shop around for a second hand one.

As for CA on the Startravel... not sure on broadband images, but if you go down the narrowband route you can certainly get decent results.  Example: https://www.astrobin.com/dlrjp8/0/ 

I think the big question mark is your mount, have you experimented already on how long an exposure you can get before star trailing starts?  

 

I use the Raspberry Pi loaded with Astroberry OS on it, for the brains of the mount I can quite easily track DSO's for a few hours using the internal guider in Ekos or PHD2. I use a ZWO ASI 120MM mini attached to a guidescope for tracking. 

I use a Baader Contrast Booster to help reduce chromatic aberration. 

[Cosmic Geoff]

I actually use an ASI224MC camera and a 102mm Startravel on an EQ-5 Synscan mount for EAA imaging.

I think some more research would be wise before investing in a large-sensor camera.  Besides chromatic aberration, I noted that when used in daylight with a low-power eyepiece the Startravel had an alarming amount of pin-cushion distortion, which made straight television aerial elements look bent.  It works okay with the small-sensor ASI224MC, but with a larger sensor, who knows what errors may become evident?

I would think either leave well alone, or put money aside for an APO refractor in addition to a large-chip camera. 

[rickwayne]

It's not as if you'd have to replace the camera if you discovered that the scope really needs to be upgraded -- it would work just fine with the new scope.

But if you're going for deep-sky, cooling is defs worth it. Cooling per se gives you advantages in reducing thermal noise (though with quickly diminishing returns, per Dr. Glover's video). But the big win is in consistent sensor temperatures, which ensures that your calibration frames are always spot-on.

Of course I shoot with a 183, whose amp glow is the stuff of legendary horror tales. Still.

[windjammer]

I use an Atik 460EX mono on a Startravel 150 F5.  The 6Mpxl Atik sensor is about 12mm by 10mm, fits nicely inside a 11/4inch filter window.  I have used it with a 0.8x focal reducer at F4 and currently with a 2.5x barlow at F12.5 for galaxy hunting.

It works well with mono RGB filters and narrowband - I have not noticed pincushion even at F4 with Atik sensor (which admittedly is quite small by CMOS standards).  Regarding chromatic aberration, Blue is not as sharp as it could be but as someone has already mentioned, it all comes out in the processing wash.  I have an Astronomic L3 blue cut filter in the image train that truncates the extreme blue that helps a bit.  As someone else mentioned, mount fettling becomes the more important  issue.

So if you do go ahead, my 2 bits is get a cooled mono camera with a smaller sensor and you should get years of fun out of your 120.  Good enough to learn the trade anyway!  Every so often (like now!) I think about upgrading - but I cannot claim to have exhausted the potential of the current set up, not by a long way.  I am no great shakes, but here is a link to some of my pics if you want to have a look

Simon

 

 

 

[vlaiv]

I would advocate a bit different approach.

If you already know limitations of your scope - maybe you could circumvent those and get better images by changing approach?

For same sort of money as ASI533 - you can get considerably larger sensor - something like this:

https://www.bhphotovideo.com/c/product/1508687-REG/canon_3699c009_eos_m200_mirrorless_digital.html

That camera costs about the same as ASI533 - but you'll be able to bin your data x2 - to compensate what you are going to do with the scope

You are going to stop your scope to 80mm of aperture to make it F/7.5. That will reduce level of chromatic aberration to more manageable levels and sharpen up image.

Binning data x2 - will make any chromatic blur show less in final image, and you'll still have 3000x2000px images (a bit loss compared to 3000x3000px of ASI533).

[Ian McCallum]

I've decided to stay with what I have at the moment. I need more experience before I upgrade anything. The only thing that stops me is the garbage Scottish weather! ☁️🌧️🌨️☔