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Rusted

Which ZWO for solar H-a with longer focal lengths?

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Hi,

I never use less than 1200mm focal length. Often with a 2x Barlow.
150 @ f/10.  Presently using a 120MC-S [colour] with PST stage2.

I'd like to stick with ZWO but wonder if there is a clear choice of camera which will really lift my results?

290, 174, 178? Cooled or uncooled? Mono seems to be most often recommended.
Most likely to be aimed at proms until the sun wakes up. Which often needs the 2x Barlow.

Only occasional lunar close-ups.

Your thoughts please? :smile:

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I'm inclined to think the 174MM might make life easier, just for having the larger sensor and greater dynamic range could be useful on a bright target, though for lunar imaging at a focal length of 1500mm I found I ended up using very low gain and high frame rates just to keep the sensor from saturating.  It can also be used for deep sky imaging, though darks are a must to remove some quite significant amp glow from one side of the sensor.

I'd probably discount the 290MM on the grounds of sensor size.  My gut feeling is that at the focal lengths you're talking about the field of view might be a bit small for larger proms.

The 178MM I have no experience with.  I wonder if it might be better not to use a barlow in combination with this camera because of the small pixel size.

James

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Thank you both.
I kept trying to respond but my wireless connection to the observatory is highly variable.
My only reference for making a decision was seeing what highly skilled solar imagers are using.
I was hoping the 174 would be ruled out being the most expensive option.

You didn't mention Mono but Merlin suggests it will always be the best choice.
Most colour cameras can be set to Mono. Does that make them Mono cameras? Too easy?
Or is there more to it than that? Colour is always handy for the occasional planetary "snaps."
Though largely irrelevant for Solar and lunar. 

Do I need cooling for H-alpha solar? Only hot desert dwellers seem to suggest it is essential.

 

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While a colour camera can be set to mono it’s still capturing in colour And just showing the image in mono. Cooling is good for longer exposures but with a short exposure solar not a problem..
 

Quote:

“A monochrome astrophotography camera can collect more signal (light) than a color camera can. (3 times as much, to be exact). ... By design, a camera sensor with a color filter array requires you to take longer exposures to record the same level of signal as a mono camera would.“

There are threads on this.

 

Edited by johninderby
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Thank you John. What a great thread that was! :thumbsup:

Everybody chipped in with an almost overwhelming preference for mono.
I learned a great deal from it because it answered lots of questions I didn't know to ask.
The main problem I have been struggling with is that many discussions centre around short focus whole solar disk use.
No doubt I could obtain such an instrument but it may not suit my PST mods.
My preference is for capturing proms with as much delicacy and detail as I can muster.

Edited by Rusted

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I think your best bet would be to carry on practicing with what you already have and currently showing improvement. The "top guys" didn't get there just by purchasing the most expensive cameras.    😀

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44 minutes ago, Peter Drew said:

I think your best bet would be to carry on practicing with what you already have and currently showing improvement.
The "top guys" didn't get there just by purchasing the most expensive cameras.    😀

Thank you Peter for your words of infinite wisdom. :thumbsup:

It deserves an adequate response because you have been very helpful in forwarding my solar ambitions.

The "top guys" probably didn't begin from a standing start at my age.
It would only be a slight overstatement to suggest I am probably racing against time and facing an ever steeper, learning curve.
So I feel that my long lifetime of equipment poverty can now be overcome with certain judicious purchases.
I hope I can then save wasting precious years "just fiddling around" when statistics suggest I may not have many more useful years to fritter away. :wink2:

By being highly selective as to my targets I have no need to scattergun funds to try and achieve everything.
My wife is no longer a cycling widow. Thank goodness! So I am always nearby to lift, mend, discuss and carry, these days.
That is a priceless, mostly daytime, low risk hobby, which we both value. One which we both consider well worth investment in its practice and enjoyment.
Moreover, I get to share my modest solar and lunar daubs with like-minded souls for their entertainment and my own.
My lifelong, innate competitiveness has found a new and harmless outlet. And, it doesn't hurt nearly as much as a 7 hour cycle ride.
Besides, you wouldn't believe the money I am saving in new tyres, tubes, chains, all the latest gear and ridiculously overpriced spares. :smile:

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No thanks. I prefer the hunger for more modest toys. :wink2:

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Yes who would want that over the top and oversized bit of kit when you could have a handy little PST?  😂😂😂

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If you're doing solar h-alpha, mono is the way to go. H-alpha only looks at a very narrow part of the visible light spectrum in the red wavelengths. A color camera has a Bayer filter over the sensor that filters out red, green and blue light to the individual pixels. When imaging the sun using an H-alpha telescope and a color camera, the only pixels that will receive any light are going to be the red pixels. The blue and green pixels are basically wasted. Switching it to mono mode doesn't make any difference at all. The Bayer filter is still there filtering out all the light. I've used a color camera before and you'll actually notice a hash pattern, which is caused by portions of the pixel array not detecting any light.

The only plausible argument for imaging the sun with a color camera would be with a white light filter as you're getting the full spectrum of visible light and a color camera would be able to pick it up.

As for which camera to use, you'll have to look at the calculator and figure out which one is going to give you the field of view you're looking for.

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Key points:

- If you go for OSC the (typical) RGGB Bayer filter will mean that only the R pixels receive any signal (as the Ha wavelength is in the red). Thus three quarters of your pixels will be more or less black. So mono for Ha solar imaging.

- A larger sensor is helpful in framing targets, but equally consider the size of the sweet spot of your scope. There is no point in spending on a large sensor if you're going to crop out a lot of the image due to it being off band.

- Consider the resolving power of the scope (Dawes limit). If you use a Barlow to increase magnification beyond the resolving power of the scope, you're wasting your time.

- Consider the camera pixel scale (arc seconds covered by one camera pixel) vs. the resolving power of your scope. You want your pixel scale to be half the resolving power (Dawes limit) of the scope to fully sample the image, but it may ve better to have a larger pixel scale and get the whole target in the frame than fully sample a smaller part of it.

- Cooling is really not necessary for Ha solar, but if you're going to use it for deep sky too may be worth the cost.

I use a 174MM with a Lunt LS60 which allows both full disk and 2x Barlow for more close up views.

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I've been using the ASI 174 mm for a while now (definitely needs the T2 tilter) -would work well for you - fast frame rates....

I wanted to get a better FOV and went for a ASI 183mm, BUT it turned out not to be suitable for solar Ha imaging (!!!!) replaced by ZWO, and I went for the ASI 1600mm uncooled.

Just my 2c

 

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Thank you for all your helpful and useful responses. :thumbsup:
It looks as if the 174 is in my stars. Or, at least, one of them. :wink2:

John's suggestion for a truss refractor was actually not far off the mark.
I have been very tempted, for quite some time, to build a skeleton, H-alpha OTA. Just as I did a folded version of my 7".
Having greater thermal control and ready access to the internal D-ERF for alignment and cleaning would be useful.
The present, lengthy stack of extenders and helical focuser is anything but rigid. And, dare I say it, downright amateur. :ohmy:

It ought to be easily possible to extend the OTA out to a normal, collimatable, focuser base plate.
Rather than relying on a floppy, helical focuser, literally hanging in mid air. 
Adding a binoviewer, at present, is an exercise in flexure and failure.
Not that I see the sun directly in H-a any longer. Not with the emphasis on imaging.

I'd really like to use my 7" for H-alpha but at f/12 it isn't a perfect match for the PST mods.
Despite endless research, I still haven't a clue how a slower objective works with the PST.
Perhaps I'd need a reducer rather than  a GPC? :rolleyes:

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A Borg 7857 helical focuser doesn’t sag but not cheap. Not sure where you’d get one now though. Here's a setup I built for a PST mod a few years ago.

86E47D16-C1F3-44FC-A81A-EF2F79C04B95.jpeg

Edited by johninderby
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The Borg 1.25” version of the helical focuser works well.

I use it on PST mods, the Spectra-L200 and the spectroheliograph.

 

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10 hours ago, Merlin66 said:

I've been using the ASI 174 mm for a while now (definitely needs the T2 tilter) -would work well for you - fast frame rates....

I wanted to get a better FOV and went for a ASI 183mm, BUT it turned out not to be suitable for solar Ha imaging (!!!!) replaced by ZWO, and I went for the ASI 1600mm uncooled.

Just my 2c

 

I was looking at field of view: Chip width [mm]  x 3460 / focal length = FOV in arc/min.

My ZWO 120 can almost manage 14 arc/min with a 1200mm F/L.
While the ASI 174 offers 32 arc/min. Or almost twice the field of view. Bigger chip.
Both at max of course. I mostly tend to use 640x480 in SharpCap on proms.
That usually gets me 118fps according to SharpCap using the 120.

Edited by Rusted
typo

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33 minutes ago, Merlin66 said:

The Borg 1.25” version of the helical focuser works well.

I use it on PST mods, the Spectra-L200 and the spectroheliograph.

I looked for the Borg but nobody had any stock.
The Omegon felt good to start with with, but soon became sloppier.
There is also some play in the extenders despite having fitted triple thumbscrews at 120°.

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The #7315 1.25” non rotating helical is $99.....

 

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I'm in Europe. By the time the banana boat arrived here and I paid an arm and a leg for customs, freight, PO customs clearance charges and 25% VAT on top of literally everything the sun would be back in action but I would have forgotten I'd even ordered the Borg.  :wink2:

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Borg accesories aren’t well stocked anywhere in Europe. FLO does sell some Borg stuff so maybe they could do a special order.?

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