L-extreme and Samyang 135mm F2

[powerlord]

Hi chaps,

sp picked up a brand new Samyang 135mm F2 ED cheap. Gonna try it out next clear night with my 6D.

I thought I'd try it with my 2" L-extreme as an aperture reduction. what do you reckon ?

i.e. step down filter rings to 48mm, and screw in 2" L-extreme.

This will still give an aperture of F3.2, no nastly spikes and fast enough to not make exposures mentally long.

I'm sure others have tried this before, but couldn't find any examples of it. I've tried it before with my Canon 300mm F4 L, but as I screwed up and left the screen on all I got for my trouble was amp glow, so it's still an unproved idea at present.

Figured if we actually even get to see the sky at night again (as rain batters off of conservatory roof...) I'll point it at around north america nebula, sadr ?

stu

 

[geeklee]

Hi stu - As you have it already, it's worth putting on and trying it.  I've never tried a filter in front of the step down rings (I use my SY with 55mm and 49mm rings).  Here's a couple of links I'd come across before discussing the filter itself at high speed but with a different scope/lens.

https://www.cloudynights.com/topic/738985-comparison-of-l-enhance-vs-l-extreme-at-f2/
https://www.cloudynights.com/topic/775023-is-f39-too-fast-for-l-extreme-filter-filter-recommendations-for-fast-scopes/

I make 48mm F2.8125 but may have my maths wrong (135/48).  You may suffer similar but less aggressive cut off with it stopped down.

If you get an image you're happy with you'll never know what light didn't hit the sensor so... worth a go!  

30 minutes ago, powerlord said:

I'll point it at around north america nebula, sadr ?

Both good, bright options, especially North American Nebula

Edited July 27, 2021 by geeklee

[powerlord]

your right, i went backwards - as i'd read the aperture was 77mm, hence FL must be 154mm.. without realising that is clearly mince as it's a 135mm, so clearly the review meant the size of the lens hood.

huh. thats an interesting article. I don't understand why a faster scope will get less H alpha.. but if the graph is right, it's not looking good.

I'd read nothing but glowing reviews on the L-extreme, and yet that graph seems to say it's rubbish compared with the L-enchance, so not really following that tbh. Even if you have a slow scope its suggesting L-enhance gets you more H-alpha.. are they just meaning because the bandpass is much more than the L-extreme's 7nm ?

stu

[geeklee]

21 minutes ago, powerlord said:

huh. thats an interesting article. I don't understand why a faster scope will get less H alpha.. but if the graph is right, it's not looking good.

I'd read nothing but glowing reviews on the L-extreme, and yet that graph seems to say it's rubbish compared with the L-enchance, so not really following that tbh. Even if you have a slow scope its suggesting L-enhance gets you more H-alpha.. are they just meaning because the bandpass is much more than the L-extreme's 7nm ?

If you look at a filter like this

https://www.firstlightoptics.com/light-pollution-reduction/idas-nbz-uhs-dual-band-nebula-boost-filter.html

it has some graphs that show why it's designed for fast systems - the band pass is shifted.

I've used an L-eNhance filter with an OSC camera and Samyang at F2 and got plenty of Ha (did I miss some?  who knows).  As you say, it has a wider band pass so doesn't suffer so much (or at all?).  Not sure about the L-eNhance and slower scopes though, it's going to let in more of the stuff you don't want too so presumably contrast suffers...

From what I've seen, the L-eXtreme is a great filter - it may just have challenges as the speed increases from a more typical refractor  F5/6/7/8.  I haven't looked extensively for people using the L-eXtreme with the Samyang but it might not be as bad as suggested (certainly the testing was done with completely different optics). It's definitely worth giving it a go.

Edit: Just as an aside, I've used and seen dedicated mono cameras with normal Baader 7nm Ha filters capture plenty of Ha with the Samyang at F2, F2.4, F2.8 etc.  Were they missing some signal, perhaps but it still had lots.

Edited July 27, 2021 by geeklee

[powerlord]

seems to work:

 

[geeklee]

Not sure it was a question of it would work just how efficient it might be. I'm glad the filter worked on the rings and you got an image you're happy with 👍

Edited August 15, 2021 by geeklee