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FLO

Es Reid checked telescopes

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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

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9 minutes ago, ollypenrice said:

The full frame chip does, I think, need the TEC.

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

Perhaps you should get one, just to check? :evil4:

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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? :evil4:

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

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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 

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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

Edited by ollypenrice

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1 hour ago, ollypenrice said:

They do now say it will cover full frame, which generally means 35mm, so that's great.

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 😁

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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

Edited by ollypenrice
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15 minutes ago, ollypenrice said:

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.

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 😁

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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

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4 minutes ago, ollypenrice said:

But this is an industry of cats, not dogs, and is resistant to herding...

🤣

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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

Edited by ollypenrice

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12 hours ago, ollypenrice said:

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

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

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1 hour ago, ollypenrice said:

I argue, in effect, that a six inch class refractor may be all you ever need

Taking the risk of straying too far from the OP, the word “all”, here, gives pause for thought.  I’m struck by the fact that this is probably a lot more than many people could afford / lift / have room for, and also that, even if you did have one, you’d need a pretty hefty mount, and probably a permanent pier / observatory to hold it.

I’d hate to go away with the impression any of this was needed to do some good imaging.  Aspirational, perhaps, but necessary?  Certainly not. 

I should add that this is written after a particularly good dinner whilst on holiday in France, and I think that the unreasonably fine weather that we’ve experienced for the last ten days has led to an uncharacteristic streak of jealousy regarding both location and equipment for astro-imaging.   I shall, nonetheless, return shortly to the U.K. resolved to acquire my first refractor (albeit a good deal smaller than six inches.). To return to the OP, it will be E.S. Reid tested. 

Edited by AKB
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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

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24 minutes ago, ollypenrice said:

... but I'm not of the internet generation 

Yet your SGL post count is considerably higher than mine 🙂

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

Steve 

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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

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On 12/09/2018 at 14:49, FLO said:

The pre-dispatch optical bench test is provided by Es Reid. He checks the telescope's optics are well figured and properly aligned. I.e. he checks for star-shape, colour, spherical aberrations and astigmatism. In short, he ensures the telescope is a good example and performs as it should. If he finds it is not then he will correct the alignment/aberration on the bench. If this is not possible the telescope is rejected. Think of it as an additional layer of quality control. We don’t provide a certificate or report. 

Regarding the flattener, that isn’t normally included but if you want it tested please email us your request and we’ll see what we can do. 

HTH, 

Steve 

Hi Steve, just placed the order for the scope and flattener (plua a ZWO OAG). I have add the request for the verification with the flattener. Looking forward to get it here.

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