Anybody using MFT bodies for astrophotography?

Mark9473 wrote:

Max Iso wrote:

if i get a faster shorter model like a 90/500, wont using a 2x barlow essentially crop the center 40% or so, mostly cutting out the outer field curvature?

Yes that is correct (see my post above).

Just be aware that the 90/500 ED doublets don't have the same degree of correction for chromatic aberration than the more common 80/600 ED doublets (and a barlow won't change that).

Gotcha, that was my guess as well. I have been breaking this down systematically and what you guys have been saying now makes sense. I also now understand why in the AP world, aperture is said to be the limiting factor in resolution. Diffraction.

The larger the main objective, the less diffraction is present, regardless of FL. All FL really is, is magnification, similar to using an eyepiece or barlow. We can only magnify any given aperture so much before diffraction starts to limit detail, so it doesn't matter if it's FL or barlow or eyepiece, the limit for resolving power is the aperture. Beyond that you are just magnifying an already fuzzy image.

What i didn't realize before is why people in camera lenses don't think this way, but now i get it. Most camera lens users can move around. If they need more angular resolution, they can simply get closer to the subject. With AP that's not an option, so larger apertures (for less diffraction regardless of the amount and type of magnification) is the only other solution.

Also, you have to choose how deep you want to jump into astrophotography. Particularly on the Moon, with an 80/600 or 90/500 you can just take a single image with the scope mounted on a heavy duty photo tripod. The shutter speed with these fast scopes will be fast enough to compensate for the Earth's rotation, so you wouldn't need a tracking mount.

If you want significantly better image scale, by using a barlow for example, you're quickly looking at a tracking mount and a lot more effort in image processing.

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Mark

Yes this was on my mind. What if i take the frame stacking approach? If lets say im using a 100/500 with a 2x barlow (or a 100/1000mm which is F10, same thing in FOV and arc secs all things equal), at F10 i may have to bump up the ISO to get that SS fast enough to counter the rotation. Just a guess but lets say F10, ISO 1600 at 1/200 sec?

Well couldn't i stack images to just bring that noise back down? One thing i love about using a GX7 is it's full E shutter, so there is no vibration and with E shutter it can shoot at 10fps full rez. I may have to nudge the FOV along every now and then and i will end up cropping out a bit of the edges when aligning, but wouldn't that work?

I figure i could use as fast a SS/ISO as needed to really freeze the moon sharp and stack as needed for noise. The key IMO is the lack of vibration and fast FPS, it really opens doors for this kind of shooting, similar to how people stack video frames. Only this is full size 16mp frames at 10fps on a MFT size sensor.