My question is would I get better results using a 290 mm? Or continue with the 174 mm. Attached is an image of the plages from 5/19/2020 using the above combination. Click image for full size.
You'll find these two sensors compete for nearly the same thing and actually are very similar in real-world results in terms of sensitivity despite having different graphs/quantum efficiency (IMX174 has 77% QuantumEfficiency, and the 290MM has 80% QuntumEfficiency). There's also noise characteristics that are different here too. And it's due to surface area. The big pixels of the IMX174 gather more light, physically, across the 5.86um size pixel. The 290MM has much smaller pixels, 2.9um and its a smaller sensor. Less light physically hits the 2.9um pixel in the same time, if you think about comparing surface areas without context. But in context, think about the same size image circle at the same image scale on the two surfaces with the two size pixels the end result is that they receive almost the same amount of light in that sense. I have both cameras and I've done this and got the same results to confirm it, but these two essentially get the same results in terms of imaging. The real difference is having to use more glass bits and stuff to achieve the focal-ratio that is appropriate for the larger 5.86um pixels with the IMX174, and the simplified imaging train with the smaller 2.9um pixels of the 290MM. And of course the field of view difference, as the IMX174 is a larger sensor than the 290MM (that said, if you match image scales, the FOV will be nearly the same!).
So in your situation, using the Lunt 60mm at F8.3 but with a 50mm Double Stack filter making it actually F9.9, 656nm is sampled critically on the 5.86um pixels of the IMX174 at F22. So ideally, you only need a 2x barlow to achieve F19.9 which is very close to F22 and undersampling just a bit, or if you could use a 2.5x barlow to hit F24.9 is also close to F22, but over sampling a bit. Using a 3x barlow, you're oversampling considerably at F29.8 and you don't gain anything from this, it just costs you more gain on the camera to get exposure as no more resolution is obtained after the critical sampling point is met for the pixel pitch of 5.86um calculated for 656nm wavelength. If you're only using the 60mm without the 50mm double stack, and you're at F8.3, then a 3x puts you at F24.9 and it's close to critical sampling F22, or a 2.5x puts you at F20.75 which is very close to F22 for critical sampling. So your setup with the 60/50 together is ideal with a 2x or 2.5x barlow on the 5.86um pixels at 656nm and your setup with just the 60 is ideal with the 2.5x or 3x barlow on the same platform.
The 290MM's 2.9um pixels critically sample 656nm at F10.9. So if you used it natively with the Lunt 60 at F8.3, it's close, but undersampling a little bit. But it would be very hard to find a barlow that only magnifies 1.25x (but it exists, such as a Baader Glass Path Corrector that is truly 1.25x). But, if you think about it, the 60/50 combination is actually F9.9.... so its really close to critical sample limit of F10.9 on its own with nothing to be added, no barlow, no extra glass, no other surfaces involved.
The 290MM on your 60/50 operating at F9.9 is nearly critically sampling and would produce an image that is 0.65 degree x 0.37 degree and a resolution of 1.2"/pixel.
The IMX174 on your 60/50 (F9.9) with a 2x barlow operating at effectively F19.9 is nearly critically sampling and would produce an image that is 0.65 degree x 0.41 degree and a resolution of 1.2"/pixel.
Identical resolution, almost identical FOV (the FOV of the IMX174 is just a bit bigger). But again, they actually are the same image scale and resolution here in their appropriate critically sampling configurations above.
So at this point, the only difference is.... the IMX174 uses a barlow to achieve its results, more glass in the pathway, but this isn't a big deal. And the 290MM does not and just plugs in and is good to go without a barlow. The 290MM technically is a more sensitive pixel, but it's tiny so physically gets less photons in the same time as the IMX174. The IMX174 gets more photons physically in the same amount of time, larger surface area, but its technically a bit less sensitive (older tech) so they end up being nearly equal at this job as their sizes off set their sensitivities. So there's really no advantage either way.
Summary..... no advantage either way really, except that the 290MM is less expensive and doesn't need a 2x or 3x barlow to do this. The IMX174 is more expensive and needs barlows/reducers which adds to cost and complexity of imaging train. But technically no real advantage and the exposures you will get are very nearly the same. The resolution is actually the same and the image scale is the same!
Keep using what you're using.
(the 290 is useful when you want to remove all extra glass in the pathway or if using a barlow/extender effects focus position, etc, and of course, its newer and less expensive, but it actually does the same job as the IMX174 sensor does when both are used at the same critical sampling point and image scale in HA; when you're imaging at very short wavelength like 393nm CaK, this becomes more and more an issue when you're needing very, very long focal-ratios to critical sample and having exotic amounts of 3x, 4x, 5x barlows just adds to cost when a smaller pixel can do it with less)
Edited by MalVeauX, 30 May 2020 - 06:03 PM.