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sooty

Skywatcher ED80 Pro

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Currently imaging with the above scope (and pleasantly surprised with the results),on a HEQ5 Pro.

My imaging time due to houses,trees,hedges etc is around 2.5hrs if im lucky!

Therefore,am i right in thinking a faster scope would enable me to catch more data? The ED80 is around 6.4 with the reducer fitted. If so,any suggestions? Budget around 1500 max. Bearing in mind the imaging weight of the HEQ5 is around 9kg depending on which site you read!

Regards,

Sooty.

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Not as simple as that ...

With imaging you want to maximize your signal to noise ratio for given amount of time. There are two components to it - signal and noise.

Noise comes from various sources - camera, light pollution, target (this one is one you can't have influence on).

What sort of camera are you using at the moment? What is your level of light pollution? Do you have resolution that you are interested to work at (resolution being pixel scale - or "zoom" - do you want to shoot wide field, or interested more in smaller objects like galaxies)?

You can increase SNR by using "faster" scope and staying at 80mm - but that will give you larger field and coarser pixel scale. You can increase SNR by using larger aperture scope while staying at same focal length - thus keeping original pixel scale (if you are happy with it). If you are using camera without cooling (like DSLR) - you will see benefit of having dedicated astro camera with set point cooling.

If you are in area with light pollution, you will see a benefit of using LPS filter if you are not already using one.

To give best advice here, it would be very helpful if you could provide details of your setup and conditions.

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The camera i use at the moment is a Altair Astro 183C hypercam,the fan cooled version,but eventually/hopefully,the Pro version,which i could then set the cooling point.I also have various Nikon DSLR's (D300S.D90,D7200),as my other hobby is Aviation photography.

I'd say im in a average light pollution area,and use a moon and skyglow filter at the moment.Still waiting for the weather to clear up before i try a UHC filter.Also,at some point in the future,id like to try Narrowband.

Main interests are Galaxies,the wide field images i use a D90/lens combo.

Sooty.

 

Edited by sooty
missed words.

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24 minutes ago, vlaiv said:

Not as simple as that ...

With imaging you want to maximize your signal to noise ratio for given amount of time. There are two components to it - signal and noise.

Noise comes from various sources - camera, light pollution, target (this one is one you can't have influence on).

What sort of camera are you using at the moment? What is your level of light pollution? Do you have resolution that you are interested to work at (resolution being pixel scale - or "zoom" - do you want to shoot wide field, or interested more in smaller objects like galaxies)?

You can increase SNR by using "faster" scope and staying at 80mm - but that will give you larger field and coarser pixel scale. You can increase SNR by using larger aperture scope while staying at same focal length - thus keeping original pixel scale (if you are happy with it). If you are using camera without cooling (like DSLR) - you will see benefit of having dedicated astro camera with set point cooling.

If you are in area with light pollution, you will see a benefit of using LPS filter if you are not already using one.

To give best advice here, it would be very helpful if you could provide details of your setup and conditions.

And the simple answer is yes...a faster scope with lower f ratio will mean you could use shorter subs and catch the same or maybe even more data.. :)

I would look at the Skywatcher Espirit 100 at f5.5 lovely scope, but maybe a bit over budget, or you could go for the 80mm version at f5.... :)

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4 minutes ago, LightBucket said:

And the simple answer is yes...a faster scope with lower f ratio will mean you could use shorter subs and catch the same or maybe even more data.. :)

I would look at the Skywatcher Espirit 100 at f5.5 lovely scope, but maybe a bit over budget, or you could go for the 80mm version at f5.... :)

Very true, but 80mm F/5 will be 400mm FL, and not really "Galaxy material" - very good choice for wide field though. I'm using something similar - TS80 Apo + 0.79 FF/FR - F/4.8 combination.

For galaxies you want around 1.5"/pixel (or less, but stock HEQ5 will not support it with guiding precision) - if you can guide around 0.7-0.8" RMS.

Above mentioned camera has small pixels (and very many of them), so we can account for oversampling by using super pixel mode - and hence go for focal lengths in range of 650-750mm.

Would mirror system be out of the question? 6" F/5 imaging newtonian with good CC?

For maximum performance, how about 8" aperture?

https://www.teleskop-express.de/shop/product_info.php/info/p5033_TS-Optics-8--f-4-UNC-Newtonian-Telescope-with-Quartz-main-Mirror-and-Carbon-Tube.html

With optimized focuser position for this (and of course, this CC included):

https://www.teleskop-express.de/shop/product_info.php/info/p9779_TS-Optics-2--Newtonian-Coma-Corrector-and-0-73x-Reducer-for-astrophotography.html

Might be a bit above budget, and it will certainly be completely opposite of hassle free system as collimation and making sure you don't have tilt issues is going to be close to nightmare :D

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Sky-Watcher 130pds with SW coma corrector would suit your camera with 2.4micron pixels. The cc acts as 0.9x reducer so you’re imaging at f4.5.  You’d need to make sure you can guide sufficiently well at approx 0.9arcsec per pixel.....

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1 hour ago, LightBucket said:

And the simple answer is yes...a faster scope with lower f ratio will mean you could use shorter subs and catch the same or maybe even more data.. :)

 

Unfortunately this is only half correct. The idea that exposure time goes as the square of the F ratio, making F5 four times faster than F10, comes from the camera lens world in which the variable is aperture. A lens operating at F5 has four times, by area, the light grasp of the same lens stopped down to F10 so it is certainly four times faster. But in astronomy we confuse this simple story by using focal reducers which do not increase the aperture but do reduce the focal ratio. So, on targets which fit on the chip with or without reducer, you get no more objects photons at F5 than at F10. You do get a wider field of view so, if you want that for a larger object, you can say that you're collecting more object photons from more object.

But on the small object all you are doing is putting the same amount of light onto fewer pixels, effectively trading signal for resolution. 

As Vlaiv says, if you go for a scope with more aperture and the same focal length you will, indeed, reduce exposure time. But beware of claims making a simple link between F ratio and exposure time. In astronomical photography this link is not so simple. That is why professionals build very large telescopes.

Olly

PS Unfortunately the hypothetical larger, faster scope of the same focal length is going to be significantly more expensive! 1) Cost is proportional to the area of the figured optical surfaces, both sides of all lenses. 2) Cost is also proportional to F ratio, faster being more expensive. 3) Colour correction in refractors is harder to achieve as aperture increases.

Edited by ollypenrice
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Personally i'd rather have a refractor,but thats just me.Haha.

I'd looked at the Skywatcher Espirit 100 ,and also the WO 103ED,

Altair Astro 102 triplet. Obviuosly galaxy imaging is very demanding of the mount,but was hoping to maybe catch some of the fainter ones.

 

Sooty.

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2 minutes ago, sooty said:

Personally i'd rather have a refractor,but thats just me.Haha.

I'd looked at the Skywatcher Espirit 100 ,and also the WO 103ED,

Altair Astro 102 triplet. Obviuosly galaxy imaging is very demanding of the mount,but was hoping to maybe catch some of the fainter ones.

 

Sooty.

So would I. I think that at, or just below, an arcsecond per pixel you can get a decent image scale on a very large number of galaxies and quite a few will look good at 1.5"PP. This should be guidable on your mount. The lower value, an arcsecond, will only work well in good seeing, though.

Olly

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I somewhat reluctantly mention these just because you mentioned that you looked at Esprit 100, and I can't tell if image quality in these will be able to match it, but I'm going to mention them as alternatives so you can do a bit more research and see if you find them attractive (they have one point going for them and that is aperture at very close to target focal length):

https://www.teleskop-express.de/shop/product_info.php/info/p3041_TS-Optics-PHOTOLINE-115-mm-f-6-96-Triplet-APO-with-2-5--RP-focuser-1-11.html

Or

https://www.teleskop-express.de/shop/product_info.php/info/p10133_TS-Optics-PhotoLine-125mm-f-7-8-FPL53-Lanthanum-Apo---2-5--Focuser.html

Combined with this FR/FF:

https://www.teleskop-express.de/shop/product_info.php/info/p5120_Riccardi-0-75x-APO-Reducer-and-Flattener-with-M63x1-Thread.html

First one will give you

115mm aperture at 600mm focal length, 0.83"/pixel native (too low I would say), but 1.65"/pixel at super pixel mode - according to reviews that I've seen, quite a good scope, an APO regardless of FPL51 used.

Second one will give you

125mm aperture at ~730mm focal length, giving 1.37"/pixel in super pixel mode - This is most appealing as option to me, but question is, since it is ED doublet - will you be happy with it (apparently very very good one, with almost no CA, something that you are probably used to since you used 80ED).

Both scopes should be within capacity of HEQ5 but mind you, both are large scopes (at least compared to ED80).

Last scope that I can mention, but it's probably way out of budget:

https://www.teleskop-express.de/shop/product_info.php/info/p6679_TS-Optics-PHOTOLINE-130-mm-f-7-Triplet-APO---FPL53---2-5-inch-RPA-focuser.html

130mm aperture at ~680mm FL (with above FF/FR) giving resolution of 1.46"/pixel in super pixel mode - what's there not to like (except the weight and size of it - at 11kg I'd say we are pushing HEQ5 to its limits - it can be done, but it would be pushing it).

 

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Hmmm. Just as i'd narrowed it down to the Skywatcher or Altair!

You've got to love this hobby at times like this! lol

 

Sooty.

 

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TS scopes that I've listed are often sold under other brands - same optics (and sometimes full OTAs) are made in China and just branded TS, Altair Astro, Stellar Vue, ...

I would not be surprised that this scope from AA is the same as 115mm / FL800 listed above:

https://www.altairastro.com/altair-wave-series-115-f7-ed-triplet-apo.html

And this also, being pair of above 125mm F/7.8

https://www.altairastro.com/Altair-Wave-Series-125-EDF-F7.8-APO.html

To complete the set:

https://www.altairastro.com/altair-wave-series-130-f7-ed-triplet-apo.html

They differ in price due to different accessories (like focusers, etc) and profit margins.

TS also has same scope you have been looking at from AA (102 F/7 triplet):

https://www.teleskop-express.de/shop/product_info.php/language/en/info/p5143_TS-Optics-PHOTOLINE-102-mm-f-7-FPL53-Triplet-Apo---2-5--Zahntriebauszug.html

I often give links to TS scopes just because that's the place I get my stuff from, so I'm familiar with their offerings (to be honest, it's just down to postage fees for me - I can get their items shipped at reasonable price) and quality has been satisfactory so far (got two scopes from them TS8" RC - rebrand of GSO, and TS80 F/6 APO - both lovely scopes with decent optic).

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The 115 triplet is very tempting,at around 8kg, + finder guider,reducer and hypercam,should just be within the limit of my mount??.Although the 102 at 5kg will pose no such problem,easier to handle and guide.Will sleep on it me thinks!

Thanks all for the replies.

 

Sooty.                                               

 

 

 

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4 hours ago, sooty said:

any suggestions?

Hi. I used to have an ed80, as recommended by SGL. I then had an opportunity to try my dslr with one of these. It drastically cuts the exposure time, so it maybe what you are looking for. It will also go well on your mount (even better, the carbon fibre version is within your budget too). I am however no expert with anything other than dslrs so can't vouch it will work with your camera. HTH and clear skies.

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