R26 oldtimer Posted February 19, 2018 Share Posted February 19, 2018 Well..., as the title says, why aren't there any f/10 or even slower triplet apo's or ED doublets? Have apochromatic scopes turned to telephoto lenses, so need to be fast, or slow achromats are just as good? I' m getting my pop-corn.... Link to comment Share on other sites More sharing options...
Frank the Troll Posted February 19, 2018 Share Posted February 19, 2018 There are, but your going to need deep pockets http://www.zerochromat.net/price-and-contact.html Link to comment Share on other sites More sharing options...
dweller25 Posted February 19, 2018 Share Posted February 19, 2018 14 minutes ago, R26 oldtimer said: Well..., as the title says, why aren't there any f/10 or even slower triplet apo's or ED doublets? Have apochromatic scopes turned to telephoto lenses, so need to be fast, or slow achromats are just as good? I' m getting my pop-corn.... Probably because :- 1. You can get the same colour correction out of a shorter f/ratio which is lighter, shorter and therefore easier to use. 2. The trend is more towards fast focal ratios for imaging. Link to comment Share on other sites More sharing options...
DaveS Posted February 19, 2018 Share Posted February 19, 2018 Just so. The driving force for current triplet apos is for short, fast scopes, whether for imaging or visual. Skywatcher do 100mm f/ 9 ED doublets, while CFF offer longer fl versions of some of their models, at a price. As I recall the original and legendary Cooke Photovisual Triplet design often went to f/15. Link to comment Share on other sites More sharing options...
ollypenrice Posted February 19, 2018 Share Posted February 19, 2018 51 minutes ago, Frank the Troll said: There are, but your going to need deep pockets http://www.zerochromat.net/price-and-contact.html Do you really want to give this more internet exposure? Olly Link to comment Share on other sites More sharing options...
Dave1 Posted February 19, 2018 Share Posted February 19, 2018 9 minutes ago, ollypenrice said: Do you really want to give this more internet exposure? Olly They no good then Olly? Link to comment Share on other sites More sharing options...
Dave1 Posted February 19, 2018 Share Posted February 19, 2018 There is also the FrT 120dED F12.5 . http://www.frtelescopes.com/frt120ded.html . Optics made in Belgium. Sounds and looks interesting to me, if I had deep enough pockets. Link to comment Share on other sites More sharing options...
Stu Posted February 19, 2018 Share Posted February 19, 2018 4 minutes ago, Dave1 said: They no good then Olly? Very much unproven as far as I can tell. Link to comment Share on other sites More sharing options...
ollypenrice Posted February 19, 2018 Share Posted February 19, 2018 1 minute ago, Dave1 said: They no good then Olly? Do they even exist? The person behind this thing was also behind the 'Cape Newise' which sold in some quantity despite having a number of dire flaws. Peoples' fingers and wallets were burned but the person in question proved (in my view) to be quite incapable of grasping the relatively simple idea that this was his fault and not the fault of his subcontractors. The point is that the consumer does not buy from the subcontractor. The buck stops with the person who makes the sale. Regarding the Zerochromat, the designer said on here that he could upscale them to much larger apertures (beyond anything he had actually manufactured at that time.) Now you are perfectly at liberty to believe his assertion that this would be entirely straightforward - or to take my view that making a big one first before talking too loudly about it would be good policy. Olly Link to comment Share on other sites More sharing options...
Stu Posted February 19, 2018 Share Posted February 19, 2018 I've always just been frustrated by the fact that there are no review units in trustworthy hands. In theory they could be great, but that's all it seems to be currently. Olly, I actually saw a Cape Newise 8" scope at AstroFest being used to demo a somewhat agricultural mount . I very nearly spent my hard earned cash on one of these, so glad I didn't! Link to comment Share on other sites More sharing options...
Dave1 Posted February 19, 2018 Share Posted February 19, 2018 Ah I see, yes I fully agree, its best policy to test products before putting them on sale. Common sense really. There is a 10" Zachromat for sale on eBay at the moment. For the pricey sum of £10,000. Link to comment Share on other sites More sharing options...
Davey-T Posted February 19, 2018 Share Posted February 19, 2018 9 minutes ago, Stu said: I've always just been frustrated by the fact that there are no review units in trustworthy hands. In theory they could be great, but that's all it seems to be currently. Olly, I actually saw a Cape Newise 8" scope at AstroFest being used to demo a somewhat agricultural mount . I very nearly spent my hard earned cash on one of these, so glad I didn't! I considered a Cape Newise after reading a glowing review in S@N magazine but plumped for a 10"SCT Dave Link to comment Share on other sites More sharing options...
Stu Posted February 19, 2018 Share Posted February 19, 2018 1 minute ago, Davey-T said: I considered a Cape Newise after reading a glowing review in S@N magazine but plumped for a 10"SCT Dave I still suspect you got away lightly Dave Link to comment Share on other sites More sharing options...
mikeDnight Posted February 19, 2018 Share Posted February 19, 2018 40 minutes ago, Stu said: I've always just been frustrated by the fact that there are no review units in trustworthy hands. In theory they could be great, but that's all it seems to be currently. Olly, I actually saw a Cape Newise 8" scope at AstroFest being used to demo a somewhat agricultural mount . I very nearly spent my hard earned cash on one of these, so glad I didn't! I'm trying to tame my comments, so I'll say I'm so glad you didn't fall for the Cape Newise Stu. Two of the things were on loan to my local astronomy club and the optics were just monstrous! Link to comment Share on other sites More sharing options...
mikeDnight Posted February 19, 2018 Share Posted February 19, 2018 If someone is looking for a long focal length apo, they could do far worse than the Takahashi FC100DL at F9. If its absolutely necessary to go longer, then one of the FC100DC or DF F7.4 with the amazing Tak 1.6X extender Q attached will give you an optically perfect F11.8. Or if you're really bent on long FL, then the FC100DL with Tak 1.6X extender Q will give you F14.4. If larger aperture is needed then the Takahashi TSA or TOA, or an older FS 128 or 152 with their respective extender Q's attached will do the job perfectly. Link to comment Share on other sites More sharing options...
25585 Posted February 19, 2018 Share Posted February 19, 2018 40 minutes ago, mikeDnight said: If someone is looking for a long focal length apo, they could do far worse than the Takahashi FC100DL at F9. If its absolutely necessary to go longer, then one of the FC100DC or DF F7.4 with the amazing Tak 1.6X extender Q attached will give you an optically perfect F11.8. Or if you're really bent on long FL, then the FC100DL with Tak 1.6X extender Q will give you F14.4. If larger aperture is needed then the Takahashi TSA or TOA, or an older FS 128 or 152 with their respective extender Q's attached will do the job perfectly. Now there is temptation. ? ? Link to comment Share on other sites More sharing options...
R26 oldtimer Posted February 20, 2018 Author Share Posted February 20, 2018 Thank you all for your replies! Actually there is the option of stepping down a big 5"-7" F7-9 apo to >F10, but that would be a bit "expensive" and purposeless. Also, although Taks are great, they are a bit on expensive side. Again you can go down the extender - barlow way, but I don't think it's better than a natively designed longer focal length scope. Since I found that a focal ratio of 1000-1200 mm works very well for all-round visual (at least for me), and after seeing the very well priced SW 72ED, I thought that an 80-100mm doublet ED F11-F12 at that reasonable price would be great. It looks (hopefully) that mass production of quality ED doublets will sooner or later substitute normal achromatic doublets Link to comment Share on other sites More sharing options...
Ben the Ignorant Posted February 20, 2018 Share Posted February 20, 2018 Sky-Watcher made the Acuter 90mm f/10 excellent doublet apo: http://www.davidesigillo.eu/test_acuter.html Maybe you can find a used one. Link to comment Share on other sites More sharing options...
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