L-ultimate weird limitation

[powerlord]

Second time I've used L-ultimate last night with a canon 300mm L USM.

I often find the EAF on the asiair doesn't work with that as it overshoots at the start, hits the end stop and poos out.

So I manually focused with the aid of the asiair focus page. I point this out, but I believe it to be irrelevant to the issue as you can see from the subs G and B are focused.

all looked good on the subs at the time - but stacking today and looking at the result it's weird - G and B are tight and R is terrible. see attached.

I've never seen that before with L-extreme.

The first time I used L-ultimate was on my P200 and that was EAF focused. I've attached the stack from that too. You can see that that is fine.

So it would appear that the L-ultimate does not play nicely with the F4 300mm. More than that I can't say, as that is the only 2 targets and configs I've shot so far, but it's worth thinking about if you were considering getting the L-ultimate.

I have looked back through my library and compared this to the behaviour of the L-extreme with the same canon 300mm lens and it does not de-focus the red channel.

I'll talk to  FLO in case I have a duff one, but for now - heads up to folk.

these attachments are named for what they are, so you'll have to mouse hover over to see what they are I think.

red from 300mm F4:

green from 300mm F4:

l-ultimate.canon300mm.fits

red from 1000mm 200pds:

green from 1000mm 200pds:

l-ultimate.200pds.fits

red from 300mm F4 l-extreme:

green from 300mm F4 l-extreme:

l-extreme.canon300mm.fits

Edited October 6, 2022 by powerlord

[Lee_P]

Odd, I'll check my L-Ultimate data later to see if the red channel has any issues for me.

[Adam J]

On 06/10/2022 at 12:29, powerlord said:

Second time I've used L-ultimate last night with a canon 300mm L USM.

I often find the EAF on the asiair doesn't work with that as it overshoots at the start, hits the end stop and poos out.

So I manually focused with the aid of the asiair focus page. I point this out, but I believe it to be irrelevant to the issue as you can see from the subs G and B are focused.

all looked good on the subs at the time - but stacking today and looking at the result it's weird - G and B are tight and R is terrible. see attached.

I've never seen that before with L-extreme.

The first time I used L-ultimate was on my P200 and that was EAF focused. I've attached the stack from that too. You can see that that is fine.

So it would appear that the L-ultimate does not play nicely with the F4 300mm. More than that I can't say, as that is the only 2 targets and configs I've shot so far, but it's worth thinking about if you were considering getting the L-ultimate.

I have looked back through my library and compared this to the behaviour of the L-extreme with the same canon 300mm lens and it does not de-focus the red channel.

I'll talk to  FLO in case I have a duff one, but for now - heads up to folk.

these attachments are named for what they are, so you'll have to mouse hover over to see what they are I think.

red from 300mm F4:

green from 300mm F4:

l-ultimate.canon300mm.fits 278.57 MB · 11 downloads

red from 1000mm 200pds:

green from 1000mm 200pds:

l-ultimate.200pds.fits 288.94 MB · 11 downloads

red from 300mm F4 l-extreme:

green from 300mm F4 l-extreme:

l-extreme.canon300mm.fits 318.75 MB · 11 downloads

Honestly the red channel simply doent look focused. CA in the red perhapse?

[PadrePeace]

Have you tried shooting with the 300mm at F5 just to match the speed of your 200PDS?

[powerlord]

It's electronic aperture - so can't change it. Adam's right I think - it'll be CA. It's just weird that it's never been an issue with the L-extreme. I mean, you'd think red CA would be red CA. 7nm or 3nm . Hell, you'd think less change of CA with 3nm.

I wonder if the band is shifting down, but then it is still capturing Ha fine.

It's not a big deal really, as the redcat is 250mm so pretty similar FL, and it works fine. I've just previously always found the canon sharp as a tack for astro, so was just surprising.