Non tracked imaging

[Richard_B]

I have a SkyWatcher Startravel 102 on a AZ4 mount with Steel tripod. I am going to use my Fuji X-T1 via a T mount for lunar and planetary imaging by taking loads of 0.5sec images and stacking them.

I have a 2x barlow that came with the scope but it is no where near enough for imaging Saturn and Jupiter so I was considering getting an basic 5x barlow. This will work ok with the pixel size of the Fuji and is actually at about the max recommended.

Anyone got any comments on this idea. I don't have funds to buy a tracking mount or dedicated astro camera so thought I's see what I can do with the kit I have plus an inexpensicwe 5x barlow.

Cheers

Richard

[michael.h.f.wilkinson]

I have just had a look at the specs of your camera, and the pixel size is about 4.8 micron. That means you get optimal sampling of the image at about F/20, so a 4x Barlow would in theory be the right one. However, shooting at 0.5 s exposure will cause enormous trailing, quite apart from the fact that you will not be freezing the seeing at that exposure time. Normally, even on my tracking mount, I shoot Jupiter at just a few tens of milliseconds, and capture thousands of frames. For planets, I really don't feel the camera you have will work well. A proper planetary camera (even a cheap one) will get better results. For the moon, you have a better chance, because you will be able to use many very short exposures. Don't forget the moon is lit by the sun at essentially the same distance to the sun as our planet, so with a 2x Barlow, at F/10, you should be able to use very fast shutter speeds (much as you would on a sunny day).

[vlaiv]

Not to mention that ST102 is F/5 achromat that has enormous chromatic aberration - you'll shoot just a blurry mess of color rather than a planet.

[Richard_B]

Thanks for the reply. I realise the scope will have a fare amount of chromatic aberration but thought I'd have a go and see. Interesting to here about the exposure times - I'll trial a few and see how I get on.

Do 4x barlows exist?

[vlaiv]

Just forget imaging planets with this scope.

You can remove almost all chromatic aberration by using aperture mask. You can try this for visual - just observe with 2" opening on your scope cover removed and you'll see nice planets. However you'll be limited to less than x100 magnification because small aperture cannot capture details that large aperture can.

This also means that any sensible image of planets will be very tiny. Planets are imaged by taking enormous number of very short exposures and for that you really need tracking mount.

Don't bother with x4 barlow either - it will be overkill for that scope as well.

You can however shoot nice images of Moon with that scope and I think that is what you should concentrate on until you get suitable scope. Here is a moon shot with ST102 scope and DSLR type camera:

There is a bit of chromatic aberration visible but one can live with that - yellow fringing on the moon surface on the right and purple fringing on the outside.

If you want to do anything serious with planets you'll want different scope - it needs to be tracked and it needs to be sharp - it does not need to be expensive. Look what Mak102 can do on moon and planets:

Do click on the image to enlarge it - view it at 100% it is worth it.

Small scope will still capture rather small planets like these:

There is no way around that - if you want larger images - you'll need larger scope.

 

[Richard_B]

Ok, thanks for the advice. I'll have to start saving for a tracking mount.

I assume DSOs are out of the question.without a tracking equatorial mount.

[vlaiv]

1 minute ago, Richard_B said:

Ok, thanks for the advice. I'll have to start saving for a tracking mount.

I assume DSOs are out of the question.without a tracking equatorial mount.

You can always try to do simple DIY option like barn door tracker or EQ platform.

These won't be precise so you'll have to limit your exposure length to something short - like 5s or so and take plenty of them.

Good thing is that ST102 can be used to do DSO photography. It won't be easy thing to do since it is fast refractor with rather poor focuser, but there are youtube videos on how to get the most out of the focuser (tighten it up and such).

Here is example DSO image taken with ST102:

Trick with removing chromatic aberration is to use Yellow #8 wratten filter and aperture mask. I think this was done with 66mm mask. Yellow filter obviously affects color balance but you can fix that in post processing.

Just accept that you'll have to do wide field shots that won't be particularly sharp due to DIY tracking and you'll be ok. I think it is not bad way to get into AP - you'll learn the technique and processing which is just as important as good tracking and good scope.

[happy-kat]

Not all all.

For planets and the Moon you should ideally shoot video and not stills. Registax can be used to process the videos.

Have a look here for pushing the boundaries of using a static mount and a telescope.

https://stargazerslounge.com/gallery/image/35963-whirlpool/

And here is an example of a static mount and a camera with camera lens.

https://stargazerslounge.com/topic/340692-summer-triangle-lite/

 

 

[Richard_B]

Wow, thanks both, all is not lost then😊 just need so clear skies and time to play.