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Optical Tube and Camera Decisions

Astrophotography Equipment Refractor CCD
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#1 jrad517

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Posted 08 April 2021 - 12:38 AM

Hi and sorry for the long post. I’ve been toying with astrophotography for a while now and would like to get a little more serious about it. My current equipment includes a Celestron 8se mounted on a Skywatcher AZ-EQ6 pro mount (my first step in getting serious), and an aging Nikon D90 DSLR. I also recently acquired a ZWO ASI224MC, with the intent to use it for planetary imaging (have not had a good opportunity to try yet) and possibly auto-guiding, although it may quickly become obsolete based on my purchase intent below. i’m hoping it can at least function adequately as an auto-guider (granted not ideal, but a different topic).

 

Anyway, i’m now looking to make two significant purchases that i hope will bring my setup to respectable DSO astrophotography status, and have some questions. The first item is a decent wider-field optical tube; and the second is a decent main astrophotography camera.
Starting with the optical tube: without getting into the details (price, fov, etc.) i’m narrowing in on either the Esprit 100ED or the EON 115ED. The Esprit seems like the nicer scope (better ED glass, focuser, includes more stuff), but seems to be a little too-wide when paired with the cheaper camera below, according to the CCD suitability calculator. The EON is larger, brings the CCD suitability more in line, and is cheaper too…but has slightly lesser quality ED glass and i’ll end up having to purchase a few additional things. It’s also unclear exactly what field flattener is correct for this scope, and if I put a reducer on, I may invalidate the narrower FOV (and thus the CCD suitability?).
The two cameras i’m looking at are both monochrome ZWO (I originally was eyeing the ASI294MC, but have become convinced mono is the way to go). The first is the ASI294mm. it seems nice and the unlocked bin1x1 helps with the CCD suitability on the Esprit 100, but I don’t understand why it’s marketed as 2x2 default. it feels like the 1x1 is not really intended to be used, or comes with some undesirable consequences. I’m also concerned about the amp-glow and narrow-band blotting I see people talking about. While it’s a lot less expensive than the second one i’m looking at, it’s still a LOT of money to pay for a camera whose whole purpose is to record highly sensitive images but then pollutes them with noise (yes, I understand it ‘should’ calibrate out).
The second camera is the ASI2600mm. Ignoring cost, this one is a no-brainer. It’s passes the CCD suitability in either optical tube, eliminates amp-glow, and has an integrated dew heater (something i definitely struggle with). But it’s ridiculously expensive, especially for someone with no history of high-quality images yet.

 

Finally my questions…the Esprit paired with the 2600 is just too much. So, option 1 is the Esprit100/294mm. Option 2 is the EON115/2600mm. Maybe option 3 is EON115/294mm (the cheapest, and I could splurge on better filters). Although other brands are still options that i’m researching, I think it might be illustrative to me to understand which of these options would be best (produce the best images) here. How important REALLY is the CCD suitability thing? the Esprit100/294mm is 2.48”/pixel even in bin1x1. How much of a difference does the slightly better FPL-53 vs FK61 (FPL-51) ED glass really make? Would the fancy 2600mm be a waste with the cheaper EON115? Am i obsessing over details that are just not that important, and option 3 would produce wonderful results (especially for someone with not a lot of experience yet. I do have some experience though, and don’t want to spend a lot of money only to be disappointed with improper equipment (yet again). This opportunity to purchase doesn’t come along often and I need room to “grow” with the acquisition and post-processing aspects without hitting equipment limits.
Any help is greatly appreciated.



#2 asanmax

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Posted 08 April 2021 - 06:22 PM

That is a million dollar question you are asking. No jokes.

I think you are going in the right direction with your thoughts.

 

First of all, I would think about the arcsec/pixel ratio. It's been proven empirically that the best ratio is between 1-2 arcsec/pixel depends on seeing conditions.

It depends on the sky quality in your area, high/low altitude, close proximity to large water bodies like ocean, air turbulence.

I live by the ocean at the sea level and seeing is never perfect here. I am getting good results at around 1-1.5 arcsec/pixel, great results at 2 arcsec/pixel.

 

When you decide on that, just choose some OTAs and cameras that you like and do the math. Try to see which OTA and camera pairs would work best together.

This is how I would do that.




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