ollypenrice

I'll be studying this with interest, Steve, since I have never been able to get any sense out of deconvolution (other than with a small format 8 bit system in an old copy of Astra Image which I once had.)

Thanks for posting.

Olly

Edit Corrected the name of Astra Image.

I'd read this characteristically excellent article by Jerry Lodigruss. Seagulls are in there!

http://www.astropix.com/html/i_astrop/Diagnosing_Trailed_Stars.html

Which looks like a 'best fit' with your problem?

The fact that a scope is new doesn't mean you should expect it to be collimated after delivery. This is unlikely, alas.

Olly

Just now, TareqPhoto said:

Are you talking about mine?

Yes. It was incredibly difficult for plate film photographers to manage the dynamic range of M42.

Olly

Within my own lifetime this would probably have been the best M42 ever taken. AP has made pretty incredible progress.

Olly

Spot on. A fine image.

Olly

Until reading this, the best job I ever heard of was, 'Fish warden on the upper reaches of the rive Wye.' This beats it!

Olly

46 minutes ago, popeye85 said:

Can someone please explain how setting circles work? And how useful they would be on a dob. I have always just star hopped to find targets 

There are two positioning systems used in astronomy. First there's RA and Dec, in which an object's co-ordinates never vary because the scales are 'printed' on the celestial sphere, so to speak. RA and Dec are the setting circles of an equatorial mount. The other co-ordinate system is Alt-Azimuth in which the scales are locked to the observer's location. To use Alt Az co-ordinates you'll need a planetarium software into which you've keyed the time, the date and the location of your setup. Your object is always moving relative to Alt and Az, the more so the further from Polaris you stray, but the planetarium will, at any given time, provide you with the Alt Az co-orodinates for the object. They are of temporary value but they will tell you the compass bearing and elevation of the object so that you can find it, after which you'll need to track it by hand.

Steve's system is very elegant. I missed that article. 

Olly

On 14/10/2018 at 13:58, JamesF said:

Just discovered a slight negative side to using metal sheeting for the roof: the cost of delivery.  Even the closest place I've found so far want to add over 25% to the order for delivery (because it's a fixed price and I don't need that much).  I might have to look at how practical it would be to pick them up.

James

I pick mine up on the Duster's roof rack. Just be careful to prevent the sharp edges from sawing through any tie downs that you use. This certainly happens, as I know!!! 

I've used flat steel sheet on our summer kitchen's fixed parasol but you have to bolt it down only at one end and hold the rest down under wooden or steel strips which allow it to expand without buckling. Why does corrugated steel not buckle along its length? Maybe it tries to but the corrugation simply prevents it. Expansion in the other axis can be absorbed by deepening the peak to valley, of course.

This is a great observatory in the making. 

Olly

1 hour ago, kirkster501 said:

I put some of these videos up, I did them when my late wife was very poorly in 2013.  I sold the RC long ago but never really had an issue collimating mine once I got the hang of it.  There are three planes that need to be in sync.

1.  The focuser needs to be aligned with the primary (not possible when an adjustment ring to do this is not provided as default on the cheaper RC scopes)

2. Align the secondary with the primary. 

3. Then realign the primary with the secondary to produce concentric circles on the wall.

Having said all that, you can get 99% of the way there, much more conveniently, with a Cheshire - as I also describe on the videos.  Once you get them collimated they will stay that way for months.  I could deliberately wreck the collimation on mine and get it back within 20 mins or so, most of the time.....!  As I explained to people, no one is going to die if you get it wrong...  You won't break anything!  It's twisting a few screws! Remove the emotion and work the problem as we say in engineering....

However,  I agree, this is all too much for a beginner - a refractor is the way to go.  With a refractor, you know any issues with your images cannot be attributed to collimation.   

I think RC scopes are more trouble than they are worth for an inexperienced imager, despite the apparent attraction of a largish apperture for reasonable cost.  

We looked at your videos, Steve, but the scope we were working on didn't follow the pattern. There were interactions between adjustments which sent us round in circles. Perhaps there was a maechanical problem somewhere.

Olly

I had an RC here belonging to a guest. We read the manuals, we watched the videos, we understood the theory, we had the tools (Howie Glatter) and we could not get it right. Random effects prevented the process from behaving as anticipated. One adjustment interacted with another unpredictably. 

For me, life is too short and rafractors are too good.

Olly

15 hours ago, JamesF said:

 

@ollypenrice has long been a proponent of the welded frame rolling roof, though I'm not sure he ever had something quite this large in mind

It was my plan to lift the roof into place as soon as I'd finished, but I'm lacking "volunteers" to help lift it this afternoon, so that may have to wait until the weekend.

James

That's a great use of the material and I wouldn't hesitate to go for it as you've done. Mine's about 2.2 x 2.5 metres and has resisted everything including a flight and crash landing when two crappy anchor bolts turned out to be tat and sheered in a violent wind. Once picked up and put back on, the steel chassis was entirely undamaged.

Regarding the roof material, I'm totally and unequivocvally wedded to corrugated galvanized steel and won't entertain anything else here, having tried the usual alternatives - all of which are flawed. Corrugated steel is totally waterproof, effectively everlasting and can be bolted down hard so it will neither tear through its anchors nor fly off. While it is noisy inside as the rain hammers down on it, the idea that it makes a noise audible outside is pure mythology. Next big job here will be to get rid of the useless rubbery-plasticky corrugated sheets on the big robot shed and replace them with steel. In less than five years the synthetic ones have started to tear off and distort while my oldest steel roof, which will be fifteen next birthday, is still absolutely perfect. I just have rigid insulation panels on the inside to counter the condensation. 

Our system here is to house our astronomers in the farmhouse: how many bedrooms will you install under that magnificent roof in the observatory??? 

Olly

I think that's lovely. There is no getting away from the subtlety of genuinely three channel colour images. 

Olly

13 hours ago, Greymouser said:

I was under the impression that they were only a 50 degree FOV, is my assumption wrong?

No, you're correct but I believe that this EP is gives the widest FOV possible in 1.25 format.

There's a discussion here. It seems to me that the conclusion (you'll never find a consensus on CN!) is that the 32 TV Plossl will go as wide as is possible at modest cost, especially second hand. https://www.cloudynights.com/topic/510769-which-eyepiece-is-best-for-the-widest-possible-view-in-125-inch-size/page-2

The best bet, though, apart from cost, is to go for a 2 inch back and a long FL ultra widefield EP. 

Olly

Edit: keep exit pupil in mind. Divide the EP's focal length in mm by the telescope's F ratio.

3 hours ago, Greymouser said:

You are not the first to suggest this and I had in fact been considering that, but for two reasons, it could be a possibility. The cost would be considerable, to put it mildly and any field flattening correction would then be lost, unless you can then buy another correcter for the two inch visual back? I wish I could afford it though, especially the top of the range eyepieces! ??

Yes, 1.25 is cheaper. In our 14 inch SCT we use a 26mm Nagler which gives clean stars to the edge to my eye. Probably the widest format you could obtain would be with a 32mm TV Plossl though there will be comparable modern EPs these days.

Olly

Unless the design of the scope has been altered I think you can acheive the same FOV without the reducer as with it if you have a 2 inch visual back. The field is limited by the baffle tube in both cases so it can be reached with a widefield 2 inch EP at F10.

Olly

It's not a mistake, it's inevitable. What is out there is too gorgeous to ignore.

Olly

Scroll down this thread to Sara's link (Swag72) for the 'too near/too close diagram: 

This should be helpful.

Olly

4 minutes ago, FLO said:

Yet your SGL post count is considerably higher than mine ?

I hope one day we can meet, in the real world. 

Steve 

Ah, SGL is real, being made of real people! It accounts for about 98% of my internet existence.

It would, indeed, be good to meet up. I would love to attend the star parties but, obviously, they happen when I'm working. The moon has the unfortunate habit of scuppering everyone at the same time...

Olly

38 minutes ago, FLO said:

It is good to hear you consider Nik Szymanek’s review of the Esprit-150 trustworthy ?

For the record, our Esprit-150 product description has included the 44mm imaging circle specification together with an excerpt from Nik’s review, and a link to the full review, for several years. 

Steve

I did check your website when looking for info on the image circle and didn't find this, but I'm not of the internet generation and am capable of missing a virtual bull in a virtual china shop. My apologies. I've also been guilty of giving too much credence to Tak's claim of 44mm as being able to cover a 35mm (long side) chip. I'm coming to the conclusion that Tak's 44mm claim for the Baby Q is erroneous - a generous term. It seems that Sky Watchers' 43.26mm are significantly bigger than Tak's 44mm so good for the Esprit.

All this gives me yet another reason for saying that I'd certainly buy an Esprit 150.

Olly

I'd like to clarify that my recent Astronomy Now article, in which I argue, in effect, that a six inch class refractor may be all you ever need, was not written as a eulogy of the TEC 140. It just happens that this is the refractor I have. I don't doubt for one moment that the Esprit 150 would have supported the same argument. 

Olly

15 minutes ago, steppenwolf said:

What we really need is a proper standard that we can judge these telescopes by as although I absolutely agree with you that ' we don't know these things till we try them ' it is a little late for that once you have laid your money down! It is difficult to understand how a corrected image circle of 44mm (which SW also quote) won't cover a sensor with a diagonal of 43.26mm on the Tak. Either the measurement is wrong or the 'standard' by which a corrected field is judged is not what you and I would like it to be!

There is a second issue here to which I don't seem to be able to find an answer. To the best of my knowledge, a 'corrected' image circle of 44mm refers to the 'flatness' of the field in terms of correction for field curvature. This does not necessarily mean that there is no light fall off from the design of the optics, leading to a vignetted image - even a vignetted image has light into its corners hence flat calibration restores the balance. Is there a standard reference for an image circle that perhaps has a particular percentage of light fall-off?

We astrophotographers either worry too much or have too much time on our hands ?

Nobody at all would have accepted the elongated, curved stars which Yves and I found using two different Baby Qs and two different Kodak full frame cameras. Neither instrument got anywhere near to covering these chips and this was unconnected with flattener spacing since we were working at native FL.

I agree that vignetting and field curvature are unconnected. Our pair of old Fluorite FSQ106s certainly have a considerable light fall-off into the corners, though the stars are good. Flats do handle the fall-off which is considerable, around 23,500 for the centre against 19000 for the corners. The filters may contribute a little to this.

I think that there should indeed be an unequivocal industry-wide standard specifying field curvature and light fall-off. But this is an industry of cats, not dogs, and is resistant to herding...

Olly

31 minutes ago, steppenwolf said:

That's interesting, as I think of the corrected image circle in terms of the sensor diagonal, not the long edge - in this case 43.26mm which according to Sky-Watcher's blurb is achieved with the Esprit 150. Personally, I'd have either telescope in shot ... oh hang on ........ I did ?

The trouble is that we don't know these things till we try them. Tak claim 44mm for the Baby Q which, you might think, would cover full frame for the reason you mention. However, it doesn't, so either 44mm isn't big enough or Tak are incorrect. I think the Kodak 11 meg is actually closer to 36mm but even this information isn't consistent 'out there.' This led me to think that 43.2 wouldn't be big enough but, it seems, it is.

Anyway, the Esprit will cover a DSLR 35mm chip and that means the new CMOS cameras as well - so all is good to go!

Olly

11 hours ago, FLO said:

Okay. I’ll bite ?

I think you’d be surprised, Olly, at how flat and evenly illuminated the Esprit-150’s full-frame imaging circle is. 

But you are right, of course. If someone has a camera with a sensor larger than full-frame (a very small and expensive market!) then the TEC140 is better-suited. 

Steve 

It would help if SW published the details of the corrected circle! They do now say it will cover full frame, which generally means 35mm, so that's great. The only 'real world' camera which might need more would be the one using the 36x36 mm Truesense chip. (From memory I think that this claim is a fairly recent addition to the SW literature but I might be wrong. I remember looking for this info some time ago and not finding it but I can't find my slippers or my mobile either...)

I think the Esprit 150 is a great refractor and, as I said earlier, I'd certainly buy one.

Olly

Edit: Yes, you are absolutely right. Nik Szymanek, who can be trusted, tested the Esprit 150 with a full frame DSLR and found it covered the chip perfectly. My apologies for questioning this.

http://www.opticalvision.co.uk/documents/107.pdf

10 minutes ago, Stub Mandrel said:

FLO do a 3" Feathertouch focuser for the Esprit 120 and 150.

Perhaps you should get one, just to check?

I wasn't thinking of vignetting but of well illuminated and well corrected circle. That of the TEC, for instance, exceeds the size of any chip I'm ever likely to be able to afford. But, if you don't need it, you don't need it - and the Esprit would give you more aperture for less dosh.

Olly

On 09/05/2018 at 15:10, FLO said:

 

 I am not aware of any other range of triplet refractors that perform as well, certainly not at the price Esprits sell at. 

The Esprits are certainly exceptionally good at the price. Often it's the size of the corrected circle which distinguishes the alarmingly expensive from the merely costly! I use two cameras in my TEC140, a small format and a large. I'd be perfectly happy to accept that the small one would probably do even better in an Esprit 150. The full frame chip does, I think, need the TEC.

Would I buy an Esprit 150? Is the Pope a Catholic?

Olly