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Who uses their refractor without a diagonal?


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On 4/18/2017 at 21:01, Timebandit said:

 

I suppose that really speaking a purist refractor set up should not have a diagonal. As to look at the target directly then you should only have the lens of the refractor and the lens in the eyepiece. This way you are actually looking at the target. 

When you introduce a diagonal into the optical set up then you are introducing a reflector into the optical chain. Therefore instead of looking at the target ,with a diagonal in the optical set up you are looking at a reflection of the target?

I hope the Dob Mob are not reading this threat otherwise they will go on about us refractor folk really using reflectors to gain our views , and in that case may as well get a reflector newt?.  

High quality prism diagonals like the Tak prism are a good purist tool :). Very low scatter and pure refracting!

As for the topic of not using a diagonal, I've tried it, and it did hurt my neck a bit, then again so do binos and I still use them. There are ways around this I know so might try again at some point :)  

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14 minutes ago, Chris Lock said:

High quality prism diagonals like the Tak prism are a good purist tool :). Very low scatter and pure refracting!

As for the topic of not using a diagonal, I've tried it, and it did hurt my neck a bit, then again so do binos and I still use them. There are ways around this I know so might try again at some point :)  

A very high tripod would help ?  :)

Try looking through just the prism in the daytime at say a sunny garden.  The view is crystal clear, apart from dust motes & FOV it is really difficult to know its in the optical path in front of your eye (I hope the neighbours don't watch me on my days off by the way). 

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On 18/04/2017 at 16:09, DirkSteele said:

However, if I had one of these I might consider it more often!

58f62c39c1792_StarChair.thumb.jpg.df8217951790746f0ce704aa7a1e8f52.jpg

Does this thing automatically track? It should do. You could be observing Vega and a few hours later be tipped out on the grass. 

 

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47 minutes ago, Chris Lock said:

High quality prism diagonals like the Tak prism are a good purist tool :). Very low scatter and pure refracting!

As for the topic of not using a diagonal, I've tried it, and it did hurt my neck a bit, then again so do binos and I still use them. There are ways around this I know so might try again at some point :)  

 

If a remember correctly Bill paolini did a review of diagnals, including some prism, including Tak . And from what I can remember then he concluded that "straight through observing" in regards to scatter on Jupiter and stars where clearer and better. Maybe it's not just in the Japanese folks and my head. Maybe it's time to get the diagonal out of the optical path if you wish the best views possible (may be not the most comfortable though). As the scope set up is only as good as the weakest link in the optical chain. Time to retire those diagnals me think's?

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33 minutes ago, jabeoo1 said:

A very high tripod would help ?  :)

Try looking through just the prism in the daytime at say a sunny garden.  The view is crystal clear, apart from dust motes & FOV it is really difficult to know its in the optical path in front of your eye (I hope the neighbours don't watch me on my days off by the way). 

I have a 16" pier extension!, but erm just the slight issue of no refractor...currently :( 

I do want another Tak prism so will give that a go when I pick one up, I'm slowly getting my new neighbours used to my strange ways ;) 

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11 minutes ago, Timebandit said:

 

If a remember correctly Bill paolini did a review of diagnals, including some prism, including Tak . And from what I can remember then he concluded that "straight through observing" in regards to scatter on Jupiter and stars where clearer and better. Maybe it's not just in the Japanese folks and my head. Maybe it's time to get the diagonal out of the optical path if you wish the best views possible  get(may be not the most comfortable though). As the scope set up is only as good as the weakest link in the optical chain. Time to retire those diagnals me think's?

From what I can tell just reading this thread, folks seem pretty split when it comes to the benefit of not using a diagonal. Might be an idea for us to all try with and without then compare notes?....I'll join in when I have a frac and a diagonal! :lol:

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1 minute ago, Chris Lock said:

         ....I'll join in when I have a frac and a diagonal! :lol:

 

I suppose it would help to have a refractor and a diagonal when we are in a post           

"Who uses their refractor without a diagonal" ?

?

 

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1 minute ago, Timebandit said:

 

I suppose it would help to have a refractor and a diagonal when we are in a post           

"Who uses their refractor without a diagonal" ?

?

 

Touche! :) Well in my defense I did have both of those things until just the other day, I had to send my new Bresser 90mm f/13 back due to it's large plastic content! even including a short plastic clam shell clamp for a 1200mm FL scope! But hey that's another story :) 

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27 minutes ago, Timebandit said:

 

If a remember correctly Bill paolini did a review of diagnals, including some prism, including Tak . And from what I can remember then he concluded that "straight through observing" in regards to scatter on Jupiter and stars where clearer and better. Maybe it's not just in the Japanese folks and my head. Maybe it's time to get the diagonal out of the optical path if you wish the best views possible (may be not the most comfortable though). As the scope set up is only as good as the weakest link in the optical chain. Time to retire those diagnals me think's?

The trick is not to have a diagonal that's a weak link! ☺

From what I remember of Bill's review, the Tak prism came a close second to the Baader Zeiss prism, and was better than any of the mirrors. All I can say for certain is that mine deliveries textbook star images even at very high power, and planetary detail is impressive. I could be coaxed into using a Baader silver diagonal, if someone would like to buy me one. :icon_cyclops_ani:

Mike

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14 minutes ago, jabeoo1 said:

I will be up for trying it out,  but I think I will very hard pushed any difference.  Seeing conditions is king here in the UK, without them we are nothing. 

This is a very good point! does the difference with and without a diagonal even come close to the effect of all the rubbish in the atmosphere? Jet streams, scintilation, dust, LP, moisture etc

Although, I guess there is no harm seeking the best for whatever particular seeing there is :) 

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6 minutes ago, jabeoo1 said:

I will be up for trying it out,  but I think I will very hard pushed any difference.  Seeing conditions is king here in the UK, without them we are nothing. 

 

Yes , time we had a SGL star party in Las Palma's. Get these refractors set up and see what our kit can really do in great seeing conditions. We can compare notes first hand over a beer and some great seeing conditions. Always fancied putting my Chinese  offering next to one of those Taks, and seeing with my own eyes if there really is that much difference in quality of view compared to the extra cost☺

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4 minutes ago, Timebandit said:

 

Yes , time we had a SGL star party in Las Palma's. Get these refractors set up and see what our kit can really do in great seeing conditions. We can compare notes first hand over a beer and some great seeing conditions. Always fancied putting my Chinese  offering next to one of those Taks, and seeing with my own eyes if there really is that much difference in quality of view compared to the extra cost☺

That would be a very interesting to see! I think I know the answer under those perfect conditions and at high mags! Mr Strehl value comes into play here. I do think the Chinese offerings are very well suited to UK skies though :)  

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44 minutes ago, Chris Lock said:

That would be a very interesting to see! I think I know the answer under those perfect conditions and at high mags! Mr Strehl value comes into play here. I do think the Chinese offerings are very well suited to UK skies though :)  

 

Any idea what the strehl figure is for a Tak FC 100 DC is (use MikeDnights) for example 

And the SW equinox 120ed Apo. Obviously a bit more aperture on my side, but I think I have heard Mike pushing his to 100x per inch and still getting cracking views.

If that's the case my Chinese offering may need to bow out disgracefully? 

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6 minutes ago, Timebandit said:

 

Any idea what the strehl figure is for a Tak FC 100 DC is (use MikeDnights) for example 

And the SW equinox 120ed Apo. Obviously a bit more aperture on my side, but I think I have heard Mike pushing his to 100x per inch and still getting cracking views.

If that's the case my Chinese offering may need to bow out disgracefully? 

Ok before I answer this, I'll point out that I'm happy to be corrected :) The Synta ED's will be diffraction limited, i.e 1/4th wave .78 Strehl and above. Due to mass production at a relatively good price you could argue that QC will let this value vary quite a bit perhaps?

I've seen APM test reports at 0.97, 0.98 but not specifically seen a test report from Tak I don't think? I do here that APM and Tak compare very well together when scrutinised, so expect that the Strehl for Tak's would typically be in the high 90's. 

As said though I'm happy to be corrected and would be keen to see a Tak test report, the happy owners do suggest it would be very very high on the Strehl rating.

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Ok, that was easier than I thought, I just Googled "Takahashi test report for Strehl" on Google images. looks to be typically around 0.98!

Here's an interesting look at Strehl's of various scopes including several Tak's that are right up there!, and the flap ship Skywatcher Esprit's that also have a fairly high 0.90 to 0.94 Strehl! 

http://interferometrie.blogspot.co.uk/

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23 minutes ago, Chris Lock said:

Ok before I answer this, I'll point out that I'm happy to be corrected :) The Synta ED's will be diffraction limited, i.e 1/4th wave .78 Strehl and above. Due to mass production at a relatively good price you could argue that QC will let this value vary quite a bit perhaps?

I've seen APM test reports at 0.97, 0.98 but not specifically seen a test report from Tak I don't think? I do here that APM and Tak compare very well together when scrutinised, so expect that the Strehl for Tak's would typically be in the high 90's. 

As said though I'm happy to be corrected and would be keen to see a Tak test report, the happy owners do suggest it would be very very high on the Strehl rating.

 

O well I may as well go chuck my ed 120 in the bin ?

1/4th does not seem to good does it?. I thought I read something a while ago talking about 1/8th but that may be wishful thinking or another figure in regards to the Scott glass or ohara? Not quite sure where I saw that 

Hopefully will get some clarification as otherwise a Tak at .98 strehl, and my ed120 equinox at only .78 then I may need to start saving. It could be an expensive year ahead?

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1 minute ago, Timebandit said:

 

O well I may as well go chuck my ed 120 in the bin ?

1/4th does not seem to good does it?. I thought I read something a while ago talking about 1/8th but that may be wishful thinking or another figure in regards to the Scott glass or ohara? Not quite sure where I saw that 

Hopefully will get some clarification as otherwise a Tak at .98 strehl, and my ed120 equinox at only .78 then I may need to start saving. It could be an expensive year ahead?

lol I've always been fairly happy using diffraction limited optics, 0.8 is fine under average seeing conditions. .8 isn't at all bad!

Having said this I've got to admit it would be nice to have a 1/10th wave optic when the seeing is good but these fast ED/triplets with high Strehl are frankly out my league at the moment at least.

I get round this by liking Looong classic achros where it is much easier and cheaper to produce a high Strehl scope! The down side is that they are Looong! but I kind of like that :)   

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29 minutes ago, Chris Lock said:

Ok, that was easier than I thought, I just Googled "Takahashi test report for Strehl" on Google images. looks to be typically around 0.98!

Here's an interesting look at Strehl's of various scopes including several Tak's that are right up there!, and the flap ship Skywatcher Esprit's that also have a fairly high 0.90 to 0.94 Strehl! 

http://interferometrie.blogspot.co.uk/

 

24 minutes ago, Timebandit said:

 

O well I may as well go chuck my ed 120 in the bin ?

1/4th does not seem to good does it?. I thought I read something a while ago talking about 1/8th but that may be wishful thinking or another figure in regards to the Scott glass or ohara? Not quite sure where I saw that 

Hopefully will get some clarification as otherwise a Tak at .98 strehl, and my ed120 equinox at only .78 then I may need to start saving. It could be an expensive year ahead?

 

I think I have seen my scope on your link. All is forgiven for my equinox Chinese frac, it looks as the Scott and ohara do there job as they should. And they come out with a very respectable 96% , 97% strehl?. 

It looks like my bank balance will not take a hammering in that case, better go and get the scope back out of the bin?

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5 minutes ago, Timebandit said:

 

 

I think I have seen my scope on your link. All is forgiven for my equinox Chinese frac, it looks as the Scott and ohara do there job as they should. And they come out with a very respectable 96% , 97% strehl?. 

It looks like my bank balance will not take a hammering in that case, better go and get the scope back out of the bin?

That's really high! yes grab it before the bin lorry arrives :icon_biggrin:

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Found it! yes that's really excellent! I'll admit I'm a bit surprised by this finding. Well done mass produced ED optics, I stand corrected it seems :) 

"120/900 Skywatcher Equinox and Black Diamond Apos

These two popular 2-lensers have the same optics built in, just differ in tube and focuser.

- the Equinox having a retractable dewshield and more elegant appearance, and a good rotation system
  for the focuser using a big union nut
- the Black Diamond having the lighter but more basic tube, no fancy rotation system and bulkier.
  The optional 0,85x reducer/flattener screws directly on the focusers tube. 

The optics is made of famous Ohara's FPL-53 glass for the crown element, and an unspecified Schott partnerglass. That provides the best possible color correction using 2 lenses, at least I have never seen any better. Actually, there are some triplett Apos on the market, that do worse. Visually one will hardly see any color fringe, maybe only in the hardest tests on moon or Venus. Photographically the residual color fringe are seen on bright stars only, and easily manageable in processing the pictures. 

Here we test one random taken example of each, and it is amazing first how close they are in their properties, and second how good they are, given they are not each hand-retouched individually, but mass-produced big sellers on the market. It happens not every Friday that you pick two scopes from the shelf, and they both read more than 95% Strehl."

 

I'll be reading more of that link tomorrow!! :) 

 

again, sorry for the tangent, back to diagonals take 2!

 

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3 hours ago, mikeDnight said:

The trick is not to have a diagonal that's a weak link! ☺

From what I remember of Bill's review, the Tak prism came a close second to the Baader Zeiss prism, and was better than any of the mirrors. All I can say for certain is that mine deliveries textbook star images even at very high power, and planetary detail is impressive. I could be coaxed into using a Baader silver diagonal, if someone would like to buy me one. :icon_cyclops_ani:

Mike

Although I do see a little bit less light scatter when I observe straight through compared to my TV Everbrite mirror diagonal, I agree with you that the compromised loss in comfort is not worth! My case is very specific because 360mm of focal length is very short and the telescope is also light. Both these two features make the elevated position pretty much sustainable and still quite comfortable up to 45-50 deg high. Said this, the times I view straight through is more for fun then else. For longer telescopes, either the OTA is placed quite high (which is quite weird and potentially unstable) or the observer needs to sit. In any case, the position is likely uncomfortable for observing and inadequate for sketching. 

 

At this stage I feel the need to start a new thread about prism vs mirror at different focal ratio. :) 

EDIT:

Here you go: 

 

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Having directly compared my ED120 with my Tak FC-100DL and TMB / LZOS 130 F/9 a few times I'm in no doubt that the ED120 has a great objective :icon_biggrin:

I believe Synta went to great lengths to get the 120mm version of their ED doublet range really good before it was released. The test reports I've seen suggest very favourable strehl ratios and PV ratings but what matters is how they actually perform and the ED120 seems to do that without any doubt.

 

 

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