ollypenrice

I've had to have custom extenders made for both TEC and Takahashi rear elements and it is a bit of a pain in the wallet. It's even worse if you get it wrong, which seems likely in view of Skywatcher's state of confusion. They should also clearly state the unflattened image circle.

Atik backfocus varies from camera to camera.

I agree that getting themselves hung up on DSLRs at this end of the market is pretty daft but they're not the only ones to do it.

However, I wouldn't get hung up on using an OAG at these lengths either, though for the dual rig I dare say you'd need to guide on an image-central guidestar.

Olly

Ingenious use of the F/W as a safety stop! Don't forget something at the other end. I'm sure you won't!

Olly

Here's the scope, camera etc. reassembled with digital callipers showing FF to RW spacing.

Imaging setup 03.jpg

But just when I shall get to try it heavens knows

Weather forecast for tonight...

Weather 31st October.PNG

Well if you live in a place called 'dunks well' you're as doomed as a hangie pilot called Usher!! 

That's why I live in Etoile....

Olly

Clear skies, clear skies, clear skies. Can't send you any. Mine are great by day and a mess by night at the moment. Groan.

Olly

It does look attractive. FLO are now clarifying the chip distance, which is good. (I have just posted a light hearted proof that the Esprit 100 is more than four times the price of the FSQ106. It's in the Whole Scopes section...  )

Glass in the light cone extends the focal distance. Imagine a car wandering off to the edge of the road and putting its right hand tyres onto the mud. It will be pulled to the right by the drag on the right. Now draw a light beam represented by two close parallel lines. They enter a glass sheet at an angle. The side of the beam that enters the glass first will behave like the side of the car that goes into the mud. It behaves as if its being slowed, which it is (c is a constant in a vacuum) so it is deflected to the side of the beam which hits the glass first. Draw this for a light cone and you see that the angle of convergence of the cone is diminshed.

Well, that's how I remember it...

Olly

Good work Carole.

Where there's a will...

Olly

I think 7mm is going to waste light.

From the dark site where I live I used to use a 35 Pan in the 20 inch F4 knowing the the exit pupil was too wide, but it was what I had.

Switching to a 26 Nagler everything brightened up considerably. I don't think it was the background sky getting darker because it was dark in the Panoptic. It was the faint nebulae looking brighter.

7mm is kind of marginal since some young or good eyes can manage that.

Olly

Oh go on, I will mention the 'f-ratio myth'. Look it up on Google ...

... and just reflect on the fact that professional astronomers build ever larger aperture telescopes for a good reason.

NigelM

There is no F ratio myth if you refuse to compare two systems of different focal length when discussing the merits of aperture. If you respect this rule you are, in effect, talking only about F ratio and then we are back where we started.

I perceive the F ratio myth as 'the focal length myth.' You cannot just rescale a short focal length image to the scale equivalent to that of a longer FL image and expect it to compare. But does anybody really believe it would? I suspect that the F ratio myth is a myth!!! (Not because it isn't true but because nobody every really claims that it is...)

Olly

I come from a purely photographic background where aperture is everything (to a degree).

Since I use a camera lens for my astrophotography that still applies i.e. a 500mm f/4 lens is twice as fast as a 500mm f/5.6 lens. The focal length is fixed at 500mm for both so the field of view (FOV) is exactly the same however I only have to expose for ½ the duration with the f/4 lens than I would have to with the f/5.6 lens. That is the only benefit of course, but for me it is a very important one since I don't guide.

It is the focal ratio that makes a difference and as mentioned above, the Fastar/HyperStar systems change the focal ratio by reducing the focal length (i.e. the light is reflected off the primary mirror straight into the imager).

When I first read the title "Aperture doesn't mean diddly squat" or something similar to that, I thought what a load of rubbish, but now I (hopefully) understand where it is coming from.

I think that, in effect, daytime photographers use 'aperture' as a synonym for F ratio. The aperture control on a camera does alter the aperture (and so the F ratio) by stopping down internally, but (and herein lies the confusion) the aperture controls of the camera are specified in F stops, which are F ratios. They are not measurements of aperture. A measurement of aperture would be the mm diameter of the diaphragm. There is a perfectly good reason for this misuse of language ( ) because calibrating 'aperture' in F ratio units means that the photographer is using the terms which are useful. He does'nt care how big the diaphragm aperture is. What he needs to know is the photographic speed and depth of field that this aperture creates. (For astrophographers all is at infinity so depth of field doesn't much matter, though the shallower it is the harder it is to get everything to work, notably regarding focus.)

But it cannot be formally correct to say, 'The aperture of this system is F4.8.' The F ratio of the system is 4.8 and the aperture is the diameter of the incident beam. Common usage in photography, though, does not have it that way. However, nobody would ever describe the aperture of their telescope as F5.

They're a stubborn lot, these daytime photographers, but in astrophotgraphy this clash of calibration terminology sometimes causes confusion.

I've read many answers to questions such as that posed by the OP but never read a better answer than Jesper's.

Cath's right that increases in aperture do theoretically bring increases in resolution but within the ranges applicable in amateur AP the effect is fairly slight and can disappear if the larger/faster system suffers from the ills which sometimes do affect very fast systems. An 8 inch Hyperstar should out resolve a 4 inch Takahashi FSQ but would you put money on it doing so for real? I wouldn't.

Olly

Leica 8x42s. Expensive even second hand but out of this world. Big hit with guests, a couple of whom have taken the plunge, I think. I bought these after being handed a pair in the dark once and not knowing what they were. I wanted to find out though, that's for sure!

Revelation 15x70. Good value but, for me, tripod only.

Liddle type 10x50s. Honestly all but unbearable after the Leicas! Damn, they seemed OK before...

Olly

hmm would love to see small pixels on it too.. to see if the optics are are really nailing it.

Not sure about this, Nick. Tim's big pixels will pick up any bloat very quickly. I suspect the 11000 will be a very good test camera and Tim's a great imager. My own experience is that the 11000 is less tolerant of the optics than the 4000 with smaller pixels. I don't think the real problem with optics is resolving the finest detail, it seems to be more to do with controlling the colours and delivering a flat field.

I'm looking forward to seeing the scope in action. I always admired the original.

Olly

Borg made a 125mm F2.8(native) a few years ago, so this is not the fastest 'apo' astrograph in history, but it is probably the fastest in production.

I knew there'd be one!! Well spotted. How 'apo' it would have been, though, is anybody's guess. 125 mm is big for F5. For F2.8 it is... remarkable.

Olly

"At F3 it would surely be the fastest production apochromat in history, no?"

Hmmmm 300mm and fast, it's a nice looking scope but how much better would it be than a secondhand Canon 300mm F2.8?

Mel

This remains to be seen, but fair point... Camera lenses can be great but there are a few issues, I think, and while you do pay for things you don't need with lenses you also don't get things you do need, like focusers fine enough for astronomical use at these F ratios. Using lenses with CCD does take a fair bit of improvising while a scope is made for that one job.

Olly

This is good news. I've seen the older Pentax in action here and, although excellent and incredibly fast, it didn't have the FSQ level of colour correction. A redesign and an extra element might easily sort that. If it can hold focus during cooldown it will certainly challenge the Tak 106. At F3 it would surely be the fastest production apochromat in history, no? The later FSQs reduce to F3.6. When you consider the extreme difficulties associated with these F ratios in reflecting designs then something like this stands out clearly. F3 that just worked? Yes indeed!

Olly

I emigrated. I've always been a bit of an extremist! You get sun in the daytime as well. Highly recommended...

Olly

Carbon is stiffer and doesn't expand/contract to affect focus. But it traps heat in the tube more effectively.

Olly

My lovely new EQ6 GT is up and running. I was paranoid about the polarity - understandably. So I got a psu with a car lighter type socket. I just couldn't risk connecting the wires to my old power supply. I wonder if this mount has protection? It seems incredible that such an expensive bit of kit would not have it.

Now to repair and refurbish the old HEQ5

Expensive? Takahashi mounts at five times the price don't have it!!! I'm not saying they shouldn't, though...

Olly

Don't worry Olly, I'm a strong believer in taking on board ways and means to improve my images, I'd be lightyears behind where I am now if I hadn't listened to what people had to say about the images I'd taken!

The dark halos are easy to explain, slap dash sharpening on my behalf, more careful and thorough masking of stars, simple.

I believe the slightly misshapen stars are a guiding or balance issue. The PHD graph is as flat as a pancake but yet I still get a little drift in the DEC axis. I'm still only running the 6"RC & ST80 on an HEQ5, at a focal length of 900mm I think it is doing pretty well, but perhaps an EQ6 would serve me better.

It might not be guiding. Firstly, is the elongation along one of the axes of the mount? If it is, then that's a good candidate. Maybe flexure, also?

If not it might be tilt which has come up a lot with these RCs. The FT would nail that, I think.

Olly

Thank you for the very kind words Olly, they really are appreciated! Are you talking about a slight elongation towards the top of the image in the stars?

Yes. I hadn't 'pixel-peeped' this image (which I'm going to say again I think is splendid) when I commented on imperfect star shape. On downloading a screen grab into Ps and taking a close look I see two issues, one of them purely a processing matter. In fact seen closer up I thought the stars looked better but I took one from near the top and it measured 5 pixels horizontally by 7 vertically. This confirms a slight elongation I was seeing in the presented image. It could be guiding, it could be tilt, it could be another optical issue. It isn't at all severe but the standard of the rest of the image does mean that the observer goes straight into hypercritical mode! John's a victim of his own success!

The other thing is that there are dark haloes around some stars. This usually arises from a lack of anti-aliasing somewhere or, more likely, whole-image application of deconvolution or sharpening. I generally try to avoid processing stars through any filters whatever. I exclude them from unsharp masking etc etc. If you just stretch the image, pure and simple, do the dark haloes appear?

Cracking image. I feel lousy about saying anything critical about it!!

Olly

The galaxy there is truly outstanding, John. Hat's off, it really is something special and shows what this small scope can do. Now when you look at an image as good as this your pickiness goes up a notch (or several notches) and the stars are not perfect. They show slight distortion. Is this from the optics, do you think, or from the guiding?

In any event you have your money's worth with this instrument.

Olly

Yup, that'll be the clips. I don't see any sign of pinching, which generally gives triangular stars. You can make a small front aperture mask to confirm this. Just stop down the objective a little.

Olly

Oops, too slow.

I've used XP extensively with Artemis Capture and for guiding in AA5. I've found it perfectly stable and far better than festering Vista. Now it looks like I'll have to find some way to escape Win8 when I replace one of the observatory laptops, but waving goodbye to Vista will be a nice moment...

Olly

Damn it...

:BangHead:

Olly

The reducer will be a big help because F7.5 is seriously slow under UK skies. It's no joke here. You need to find the chip distance for the reducer first, from the vendor's website.

Then add up the following;

Front of camera to chip distance.

Filterwheel thickness.

Approx a mm for the refractive effect of the filter.

This total will be a bit less than the chip distance for the reducer so you need a set of spacers to add the missing distance. You need to check the thread on the back of the reducer and the Atik EFW2 is M54. Whatever spacers you buy need to fit these, of course. Good suppliers know all about this and should sort you out.

A tip; put some boot polish on the fine threads of all these infernal spacers or they will cold weld themselves together for eternity just before you find just the right chip distance...

A small amount af adjustability in the form of nylon shims or lockrings can be arranged and is a good idea.

Olly

Any news?

Olly