Thoughts on widefield 'scope...

[Andy01]

Hi everyone,

Her indoors has generously allowed me to buy a second widefield 'scope, (budget around $2.5K woohoo!) to compliment my existing WO FLT110.

I mainly shoot nebulas in NB, often but not always from the burbs with bimonthly dark sky trips.
I'd like to go wider than the 1.67x1.3* which my current FLT110/0.8 reducer combo will allow on my QSIwsg8 sampling at 1.81" p/pixel.

For example a William Optics Star71 will allow 2.96x2.30* - but I understand the sampling will be around 3.2" per pixel which is maybe not ideal?

A 2nd hand Tak fsq85 is almost in reach of my budget and samples at 2.47* p/pixel with a FOV of 2.29x1.78*

Of course I could also consider parting with the FLT110 which would add another 2K or so to the budget, but then I would only have the widefield scope, yada yada etc. hmmm.

Happy co consider other suggestions and would welcome input on the whole resolution v. sampling p/pixel thing.

cheers
Andy

[RickS]

Andy,

There's nothing wrong with sampling at 3 arcsec/pixel or more. Plenty of great widefields have been captured with a FSQ-106 and KAI-11000 or KAF-16803 sensor at 3.5 arcsec/pixel.

If it were me I'd be looking for more sensor real estate and bigger pixels but I'm not sure if the FLT110 has the image circle for a big chip?

Cheers,
Rick.

[glend]

Does it have to be a refractor? The Skywatcher MN190 (1000mm fl, f5.3) is within your budget and mount capacity, and a darn good astrograph with true colour rendition, no detectable coma, and no diffraction spikes. If you don't mind diffraction spikes there are many newt (& coma corrector) combos that will eat up less than half your budget.

[Andy01]

Hmm - well that's an idea I hadn't considered Rick, a new camera?

The FLT 110 came with an adapter for an STL 10000 so maybe it has the image circle required, but the budget probably won't stretch that far unfortunately, then there's 2" filters etc.



Hi Glen, no I'd consider a newt - I looked at the TAK Epsilon E130D - a mate has one and it's fantastic, but it's almost $4k.

With a FL of 1000mm the MN190 is longer than my current setup (616mm) so it has an even narrower FOV. But hey, maybe there are other, shorter newts around that are cheaper than the Tak E130D but still make decent astrographs?

[gregbradley]

I agree with Rick.

Better to get a larger sensor. You've already got about the widest FOV you're going to get easily. FSQ106ED are more like US$4300 + shipping, exchange rate and GST so more like AUD$7500.

QHY is bringing out a 16.2mp camera with OAG and filter wheel like a QSI for US$4K later this year. Its 28 x 18 or something similar. google QHY16200A.
6 micron pixels would suit widefield short focal length very well and your refractor should be able to handle that size chip without trouble.

An 8 inch F4 Carbon tube Newt would be 800mm focal length.

An STL11 comes up every now and then but they typically go for US$3800 to US$4300 depending on condition, filters, accessories.

Astro cameras are very expensive.

Greg.

[Paul Haese]

Andy you could go with an Orion CF tube Ed80 from Bintel of a Televue TV 60. With reducers it would suit your budget and still provide really good portability for nights under dark skies. No collimation issues either, but that is easy enough to sort with a cats eye collimation kit.

[Andy01]

Thanks Greg, yes astro cameras and TAKs are very expensive and I doubt the missus would understand my wanting another camera having only gotten the QSI last year!



Thanks Paul, yes the options for buying wide field triplet APO's new seem to be as follows...(the Televue is a doublet).

-Orion ED80 f6.0 480mm with 0.8 reducer/flattener at under $1800 from Bintel
-Stellarvue 80 f6.0 480mm with 0.8 reducer and a feathertouch focuser at $2800 landed probably closer to $3k with GST.
-WOstar71 f4.9 needs no flattener and is 348mm so has the widest FOV of all 3 scopes for around $1500 landed+ GST

Have to say I'm leaning towards the WO at this stage but would welcome opinions about the other candidates. :thumbsup:

Cheers

Andy

[Slawomir]

Hi Andy,

I would not recommend Orion ED80CF triplet - I have one.

Although optics are very good IMO, mechanically this telescope is not suitable for astrophotography, if you are serious about it. The problem is the carbon fibre tube - the flange that holds focuser to the cf tube is attached by tiny three screws that are screwed directly into the cf tube and patched with glue. With time, these screws start moving within the tube and you will end up with flex and optical mislignment. Replacing focuser will not solve it - I even got Moonlite hoping it will fix the issue; in the end had to do a home-fix with epoxy cement and masking tape.

Otherwise, it is a fine telescope - I use it for visual observations. I bought mine over two years ago, so Orion might have changed their design since then.

P.S. I did not intend to upset anyone with my feedback regarding the scope - I was as objective as possible.

[Andy01]

Thanks so much for the Heads up Slawomir :)

Seems it's become a two horse race between the WO star71 at $1500 + GST etc or the Stellarvue SV80/0.8 reducer/feathertouch combo for $2700 + GST etc.

Anyone got an opinion to share as to whether or not the SV is worth the extra bucks?

[AlexN]

With 2.5k to spend, I would buy a 2nd hand canon 300mm f/2.8 camera lens. It's wide, it's fast. It's designed with 35mm sensors in mind and the optics have proven themselves for astro imaging.

I just recently picked up (the second one I've owned now) a tokina 300mm f/2.8 for $900 .. If you are doing narrowband imaging with a kaf8300 sensor stars will resolve to an individual pixel at times but dithering and drizzle processing will make short work of that.

[Camelopardalis]

If you intend to use a full frame chip, then it'd be worth checking whether the SV can do that. The WO was designed for it. However, there have been a couple of reports on CN of Maltese cross shaped right stars. On the plus side, there are people out here using them with full frame chips and the images look really promising.

Camera lenses bring their own set of parameters that may or may not be ideal for AP...

[Slawomir]

No worries Andy.

What about Zeiss FE 55mm F1.8 lens? Greg has one and his shot of Rho Ophiuchi with this lens is magnificent.

Here is the link - Greg, I hope you do not mind :) http://www.pbase.com/gregbradley/image/160891607/original

[SamD]

Sorry, no help on the scopes you've mentioned, but with NB imaging at least, I've found that even inexpensive "vintage" camera lenses give pretty good results, and are fun and versatile for wide field nebulae.

Chromic aberration isn't a problem over the bandwidth of NB filters, and drizzle integration restores a lot of resolution.

Two that I enjoy using are a Carl Zeiss 135 f/3.5 and a Takumar 200 f/4, both with M42 screw fittings.

[Retrograde]

Hi Andy,

what about something like the Borg 71FL? It has a focal length of 400mm.
They also have a Feathertouch option (which adds significantly to the cost of course).
I believe it will cover full-frame when using one of their flatteners or reducers.

[Andy01]

Interesting approach Alex - I was all set originallt to get the adaptor for 6x7 pentax lenses and a 165mm and 300mm 2nd hand, until I heard that QSI had ceased production of the adaptor.



Yes, I had heard of the cross shaped, even pyramid shaped stars on CN forums, probably the only thing holding me back right now.



Slawomir, yes, see my comment above re: camera lenses :)



Yep, not sure If I want to put a 35mm camera lens on the QSI though. though, issues with image circles and covering power are often mentioned.



Wow, I googled the Borg and it does seem resistance is futile! Pricey though bet well worth further investigations. Cheers :thumbsup:

[gregbradley]

Camera lenses for astrophotography:

Nikon 180mm F2.8 ED about $500-600. A good lens a bit of chromatic aberration but correctable in processing.

Nikon 50mm F1.8G 1.8D both are very good wide open. I have used the 1.8g with a Proline 16803 and adapter successfully. Canon 50mm would be the same as they seem virtually identical as lenses.

Nikon 85mm F1.8g coma and chromatic aberration until F2.8, Most fast lenses are like that. Wideopen you get coma and or chromatic aberration which stops around F2.8 so not much gain to pay for the F1.8.

Nikon 105 F2.5 AIS is a beauty probably under $200. Metal, aperture ring, and well made.

These are all evaluated using either a Proline 16803 or STL11.
Pentax 67:

55 F4 - not bad, needs to be stopped down to F5.6 to counter coma. $100 or less.

75mm F4.5 a beauty. I used this one recently and it works really really well. $125 or so.
Perhaps a bit slow.

165 F2.8 brilliant lens, cheap, sharp wide open, no chromatic aberration one of my favourites. $200 or less.

300mm F4 $300-450 (non ED version). Good for narrowband. My adapter has a small amount of play and this can cause this lens to rock slightly making subs on one side of the meridian not match well with subs on the other side. It may be OK now as I have a later filter wheel and the adapter can screw in deeper. The one I had I needed to have it unscrewed a little bit so the adapter did not hit and stop the filter wheel filter hold in screws.

300mm F4 EDIF (around $1500) never used it but this is the one. Marco has used it extensively and I have seen other images using it. A ripper. There is also a 400mm F4 EDIF.

Zeiss 300mm. Never used one but seen images by Wolfgang Promper that are superb. Probably an expensive lens as most Zeiss are.
Pentax 200mm SMC Marc on this site uses this and lots of fabulous examples.

It depends on what you want to image. 50mm is a good all round widefield lens that are generally easy to use and most are probably pretty good as 50mm seems to be easy to manufacture.

100-200mm gets a fair bit closer in. 300mm is now like an FSQ with a reducer but smaller aperture lens. More demanding of flex and strength.

I have an adapter for the Nikon lenses from FLI. I also got a Pentax 67 adapter made up custom by Precise Parts.

Focusing can be done manually but its tricky. I used to use a FLI PDF focuser with adapters and that worked really well. The FLI Atlas would work even better.

My Zeiss FE 55mm F1.8 may or may not be suitable as Sony FE is something like 24mm backfocus whereas Canikon are more like 48mm.
The FE lenses are designed for Sony mirrorless and the short backfocus is why virtually any lens ever made will work with an adapter on Sony and Fuji mirrorless.

Modern Canikon lenses are a bit of a problem as they are electronic and most do not have aperture rings anymore so you need to jam up the little sliding prong that holds the aperture open.

Widefield nightscape lenses:

Nikon 29 F2.8 - not very good.
Zeiss FE 35 F2.8 a bit of chromatic aberration wide open. Not bad not great. Needs to be stopped down.
Zeiss FE at F4 its very nice. More wide open a bit too much chromatic aberration but this is one of the top 4 lenses listed in DXO Mark and a super sensational lens for regular photography. Super sharp. A magnificent lens.
Nikon 14-24 F2.8ED - the king of the widefields with perhaps the Zeiss 15mm F2.8 only better. The new Canon 11-24 is probably also as good if not better but very expensive. I was not able to use this lens on my Proline as the adapter spacing must be a tad off and this lens needs it to be bang on.
Samyang 24 F1.4 Good at F2 onwards. A good lens and sharp to the corners no coma after F2.

APSC;

Fuji 18-55 F2.8 a remarkably stunning lens for a kit lens. Fuji kicked a big goal with this lens.
Fuji 14mm F2.8 another remarkable lens. Metal and aperture rings although electronic fly by wire aperture. That would make it hard to put on a CCD camera.
Fuji 35mm F1.4 not bad. Not great, again you need to stop these lenses down for them to work. Astro work is far more demanding than terrestrial in this regards and you see the coma and chromatic aberrations that don't show up too much in terrestrial work.

My favourites are:

Nikon 14-24
Pentax 67 75 F4.5 and 165 F2.8
Nikon 50m 1.8g and 1.8d
Zeiss FE 55 1.8 on the Sony A7r.

I don't know a lot about Canon lenses apart from anything L and a prime is likely to be very good. Zooms of any brand except perhaps Fuji are probably a no no. I tried a Yashica Zeiss 28-70 zoom and it was not too bad but chromatic aberration required it to be stopped down a lot.

Greg.

[gregbradley]

Andy your best bet is to sell your existing scope and pick up an FSQ106ED.

It is the king of widefield scopes and is freely available. The reducer allows super wide imaging if you want to do that as well.

Nothing else really comes close except the TEC110 flourite F5.6.

I have used both. The TEC gives better colour, the Tak is more tanklike and strong. FSQ is probably the easier to use overall as its built specifically for imaging. A slight green bias could be corrected by flocking the interior if you wanted to go that route or just handle it in processing.

FSQ 106 can take any camera. Most of those smaller scopes lock you into small chips and don't have quality accessories and you could be setting yourself up for constant gear fiddle and eventual upset and selling at a loss to get one later anyway.

Greg.

[Octane]

The FSQ-106N is even better than the ED with no colour casts. :P

How about a Takahashi FS-60CB? 60mm aperture, f/5.9 and 354mm focal length. Reasonably-affordable.

If you go any Takahashi route, be prepared for the nightmare that is the adapters.

H

[Atmos]

I have been meaning to give me Nikon 50mm 1.8D a shot for astro work, still haven't really gotten there. The only real 10 second image I took with it and my D700 years ago had HUGE amounts of coma at F/1.8 so it does need to be stopped down a bit. Just look at the top left of the image, it's like a bird in flight ;)

[akiil]

-------

I second the Samyang 24 F1.4 This is by far my favorite lens! Outstanding re. no coma.

[akiil]

---
This is a single 30 second unguided sub with my Samyang

[Retrograde]

Someone with much more experience than me mentioned that Peter Tan in Hong Kong would be a good place to source one. Check out his site if you are not already aware of it:
http://www.tan14.com/gears.htm

[Slawomir]

Just out if interest, apparently Moonlite is now making 3.6" focusers (and optional rotators) for Tak scopes: http://www.focuser.com/media/Downloads/Documents/CXL%203.docx

[Octane]

Those focusers look absolutely stunning.

H

[Andy01]

Thanks Greg, good advice - yes I take the point and will probably buy a small 'scope to play with for season or two and then sell both and get an FSQ.

I've heard form a user that focus is super critical with those taks and as I use a mac and have to do everything manually, including focussing, it's unlikely to be a happy marriage at this point in time. Eventally I'll have to bite the bullet and go the PC route, but I'm not ready for that yet!

Wonderful report on camera lenses btw - may I recommend you post that in the Projects and Articles section for all to enjoy :)



mmm - was briefly tempted but was put off by the adapter thing. Doublet vs triplet, does it need a flattener? etc not sure



Thanks will email - Borg looks incredibly complicated though - wading through lots of different components, adapters, reducers, tubes, focussers etc.

So far the WO looks like the preferred complete package.

[Octane]

On a full frame camera, yeah, you'll need a flattener. On an APS-C chip, you might be OK. :)

H

[gregbradley]

I focused with an FSQ manually with an electronic focuser for years. I even used to do it manually using the microfocuser in the past.

Easy as Bro.

They are not hard to focus at all. What they are a little sensitive to is fast changing temperatures. That just means a refocus every now and then.

FSQ is king Bro (sorry for the Kiwi slang).

Greg.

[Octane]

Greg,

I got temperature compensated focusing working on my RoboFocus. It is a dream come true! I am now no longer wasting 10-15 minutes every hour in AcquireStar focusing routines.

It's not so bad with LRGB filters, but, once you start automating focus with narrowband filters, it takes ages.

I'm a happy camper.

H

[gregbradley]

I see FocusMax 4 has a temperature compensation feature. I was logging the focus positions of my Honders but it was hard to see an accurate difference per degree C. I think it was going in 75 steps out of 105000 on the Atlas. Not 100% sure. The temperature sensor on the Atlas seems slow to respond to the ambient temperature and I think that was throwing it off. Do you use an external temp sensor? That may be the key rather than one embedded in the focuser.

Sky X also has a temp compensation feature. It seems easy enough to use if you get the right temp data.

Greg.

[Octane]

FocusMax 3 has temperature compensation. :)

At the moment, the sensor is inside the RoboFocus control box.

I'll look at purchasing an external sensor in the near future.

H

[Slawomir]

I wholeheartedly recommend an external temperature probe. My Moonlites have internal probes and these are relatively slow to respond to temperature changes, while external probes are very sensitive and quick to respond to ambient temperature. It has made all the difference in my case.

[Andy01]

Ahem... Er, gents no disrespect but let's get back to the original topic.
So does anyone have hands on experience with a WO star71 or a Borg 77EDII and a CCD?

[Camelopardalis]

How about a SW Esprit 80? f/5 triplet, flattener in the box, plenty of field for your current CCD and available for under $2k :question: should give you almost 4x the field area.

I have the Esprit 100 and the pixels on my 1100D are only a little smaller than your CCD, PM me if you're interested in some example data.

[rally]

I agree, but actually the best bet is the astrophotography model
FSQ106EDXIII
The captains wheel monstrosity is useless for any serious AP

You wont need a flattener for any FSQ either

Or pickup a secondhand FSQ106N

BTW The adapter thing isnt hard - you work out what you want in the image train and buy the custom length custom made adapter/s from Precise Parts.
The only thing to keep a track of is the total back focal distance.
I wonder those new Moonlite focussers have extra back focal distance built into them - that would make them invaluable - just 1-2 extra cms is all you need !

Cheers

Rally

[gregbradley]

I'd ditch the FSQ focuser eventually and get one of these new FSQ ready models from Feathertouch 3.5 or Moonlite 3.6. They come ready to screw onto the FSQ apparently.

FSQ 106ED is a great scope but Tak messed up with the focuser. The FSQ106N focuser/focuser lock is better.

Greg.