Post by nobody on Aug 4, 2015 11:19:08 GMT -5
Hello
While searching online for a suitable achromat, for a new ATM project, I discovered iStar offers R35 lenses.
By now I must have read everything ever written online about iStar in every conceivable language.
So far I have still found no independent confirmation that the R30/35/50 designation offers better colour correction than a standard achromat.
Individual observers have such varying false colour tolerance that reviews must always be read with considerable caution.
My own Celestron/ Synta 6" F8 seems to vary in its violet haloes depending on my mood, the object and the seeing.
I have other, smaller refractors, so know enough about false colour to know what to expect from different CA ratios.
The claimed advantages for Rx optics are obvious:
A much shorter and lighter OTA is more easily stored, handled and is very much easier to mount equatorially.
This can really make or break the point of ever making a purchase in some cases.
A longer OTA has considerably greater moment and will usually disappoint on an inadequate mounting.
The [claimed] R35 colour correction is not entirely a free lunch though.
One pays a premium for the R35 optics by having to go down one lens size for much the same price as the achromat size one above.
So you lose the next larger achromat: Which offers greater light gathering power, resolution and potential power. [Plus bragging rights!]
All at the cost of a poorer CA ratio and much greater weight and bulk of the bigger lens once mounted in its OTA.
Do not read this post as remotely a criticism of iStar, its claims or any of its products.
I just want confirmation [encouragement to purchase?] that choosing the next smaller lens in R35 [rather than the next bigger achromat] will be a wise choice.
Do you own a more normal focal ratio R30/35/50 lens? I'm not talking about F5 or F6 in huge apertures.
What about 6-8" R30/35 lenses in f10-f12?
Is the R35 premium worth the investment at the cost of greater aperture in a normal achromat?
Thanks for your patience
BTW: I couldn't get the private email Contact service to Ales or Mike, on the iStar website, to work.
The addresses are HTML so cannot be used for normal emails.
Hence this rather public appeal for experienced advice.
Feel free to delete this post and go to private mail.
While searching online for a suitable achromat, for a new ATM project, I discovered iStar offers R35 lenses.
By now I must have read everything ever written online about iStar in every conceivable language.
So far I have still found no independent confirmation that the R30/35/50 designation offers better colour correction than a standard achromat.
Individual observers have such varying false colour tolerance that reviews must always be read with considerable caution.
My own Celestron/ Synta 6" F8 seems to vary in its violet haloes depending on my mood, the object and the seeing.
I have other, smaller refractors, so know enough about false colour to know what to expect from different CA ratios.
The claimed advantages for Rx optics are obvious:
A much shorter and lighter OTA is more easily stored, handled and is very much easier to mount equatorially.
This can really make or break the point of ever making a purchase in some cases.
A longer OTA has considerably greater moment and will usually disappoint on an inadequate mounting.
The [claimed] R35 colour correction is not entirely a free lunch though.
One pays a premium for the R35 optics by having to go down one lens size for much the same price as the achromat size one above.
So you lose the next larger achromat: Which offers greater light gathering power, resolution and potential power. [Plus bragging rights!]
All at the cost of a poorer CA ratio and much greater weight and bulk of the bigger lens once mounted in its OTA.
Do not read this post as remotely a criticism of iStar, its claims or any of its products.
I just want confirmation [encouragement to purchase?] that choosing the next smaller lens in R35 [rather than the next bigger achromat] will be a wise choice.
Do you own a more normal focal ratio R30/35/50 lens? I'm not talking about F5 or F6 in huge apertures.
What about 6-8" R30/35 lenses in f10-f12?
Is the R35 premium worth the investment at the cost of greater aperture in a normal achromat?
Thanks for your patience
BTW: I couldn't get the private email Contact service to Ales or Mike, on the iStar website, to work.
The addresses are HTML so cannot be used for normal emails.
Hence this rather public appeal for experienced advice.
Feel free to delete this post and go to private mail.