Posts Made By: Tom Lacovik

Hi.

Is a "49mm filter" one and the same as a 2" filter? or is it just a camera accessory?

I have a 2" TV everbright diagonal, but all 1.25" EPs (for now) connected with the adapter.

I don't enjoy unscrewing and screwing a filter between EPs all the time, so it would be nice to screw it on to the MCT (Intes MK67) end of the diagonal (the tv diagonal looks like it's threaded for a 2" filter I think on that end).

So, is that right? Can I get something being sold as a "49 mm" filter and screw it on to the MCT end of the TV diagonal, and then just swap out EPs at will to change magnification without fussing with the filter each time?

Thanks,
Tom.

PS. I am planning a mid-sized dob right now, and will eventually make some kind of filter slide for the upper cage, so probably 2" filters would be better for that too in order to avoid vignetting right?

Can anybody suggest a west coast equivalent to Spectrum...I have heard of L and L or LNL? Clausing too seems good.

Is Spectrum simply THE best, no questions asked (don't even think about anywhere else once you have a premium figure) or can any coater do pretty much the same job as long as they don't pile it on and spoil the figure.

Can anyone testify for or against LNL coatings. They are in California, and some people, especially on the west coast are using them instead of Spectrum.

I can't find a web site, maybe it isn't LNL but L&L which or worse, "L and L" but I think it's LNL. In any case all are hard to find as google search terms. But I thought someone here would have used them and could speak about the results a bit.

Thanks.
Tom.

An earlier post of mine asked about a PARTICULAR coater that no one seems to know anything about, blowing my chance for a lot of good replies (though I got 1 or 2 thanks!). So I hope you will permit me to rephrase my question, in hopes that an alternative worthy of my mirror is found on the west coast (i live in oregon)

How important is that ionizing process Spectrum uses? Can someone recommend an excellent coating company who can keep my premium (Swayze) final figure in tact without uneven application or changing my bands?

TomL

Okay, I'm not breaking any stereotypes here, but as a Canadian living in the US, I still play Ice Hockey (in fact, we are REQUIRED to always have a bag of pucks with us, no matter where in the world we live).

So this morning trying to spot Mare Orientale without much success due to early morning clouds, I thought I may as well see what all the hype is about over vibration suppression pads ($50 for three discs of rubber -- puh-leez!).

"Hey, I've got a bunch of 'discs of rubber' downstairs" thought I, so I thwapped my Nexstar 8 legs focussed on whatever I could focus on in the morning...a distant rooftop. "zero one thousand one one thousand 2 3 4 one thousand.... five, well I think it was shaking between 4 and 5" .

Four seconds to settle down to a quiet vibration, and by five, it was totally solid again. I think I got the N5 tripod with my N8, so I always blamed that and wondered if a ring mounting would be better than the single tine fork mounting, but in the mean time, tried to avoid concrete which is what I was on.

Then I put the 3 hockey pucks under the feet. Thwap! one one thousand. Solid! Hmmm...Really? TWAPP!!! One one thousand T... Solid. Hockey pucks back out. Thwap. 1 2 3 4...and 5 I guess (probably small vibes would be obvious at infinite focus on a point source at night if you know what I mean, but just staring at a roof tile, It looked like 4 to settle, and quiet vibrating for another 1 for a total of 5 seconds). THWAPPP! 4 and 5 again.

Pucks under again. Thwap again. One second again. No stop watch, but I left the pucks out of my hockey bag and in the garage with my scope because my tripod will never be without a vancouver canucks logo under its feet again! And I don't think I will need rings after all. Or even a beefier tripod. I mean if you bonk your OTA or tipod that hard, you should expect 1 second of vibration no matter what right? But you don't want to go on a motion-sickness inducing roller coaster ride every time you focus which is what it is like if your dampening times are 4 seconds or more which is what I was into. blech. Made me wish I never sold my XT8 which required a horse to kick it to really shake.

Price=zero, if you play hockey that is...sooner or later you just acquire these things usually too beaten up to use in a game, but perfect for tripods. Or just pick a few up at a rink, sporting good store for a couple bucks each.

Enjoy eh?

TomL

Hello.
I am building a dob using the Kreige/Berry book as my guide, but got a little lost in the sections on eyepiece-exit pupil-secondary size relationships. sec 4.3 through 4.5.

I am building a 13.1" whose true focal length is 58.5".

I am super partial to Pentax XL eyepieces and have 3 already (14, 10.5 and 7) looking to add something in the 18-22 range and then later something closer to 28 to 32mm. These are all 1.25" EPs and I'm even wondering whether I should just stick to a 1.25" focuser to keep the CO to a miniumum and also the weight of my upper cage as low possible (both due to a light weight 1.25 focuser and a smaller secondary?) as my base is going to be low profile (portability, nestability is my priority) so I need as light weight up top as possible to stay in balance.

With all these factors floating around though, ALL I REALLY NEED TO KNOW IS WHAT SIZE SECONDARY DO I NEED FOR THESE PARAMETERS? D=13.1 FL=58.5...and EP preference as noted above.

Thanks!
Tom L.

What is the best feeling / working dob focuser THAT WEIGHS LESS than the feathertouch. I guess there's the NGF-DX1 weighing in at 18 ounces versus FT's 21 ounces.

Low profile would be nice. Any moonlite reviews out there? Can't find em. Any experience appreciated.

Thanks,
TomL

p.s. another way of phrasing this question would have been: "any suggestions for a good light focuser for my nesting (hence the desire for low profile) 13.1" truss dob?"

Lost in the long thread below, Vlad and Mike and Newt helped me conclude that somewhere between 2.3 and 2.7 min axis for my secondary was appropriate:

"If you'd take H=0.25"+1.45"+1.5"=3.2", then your diagonal-to-focus distance would be L=T/2+H=7"+3.2"=10.2". Your min diagonal minor axis is A=L/f#=10.2"/4.46=2.3". For 0.5" (~0.5 degree here) fully illuminated field you'd need
A=2.3"+0.5"(1-L/F)= 2.7" minor axis. Illumination 14mm
off-axis is 82%, and 63% 23mm off-axis. Not much different from what you came up with. Take your pick. "

Well, I did take my pick. It took me a couple days to think through this analysis, but I see it is all correct now. One thing though, is this is all theory. In practice one doesn't find an infinite choice of secondaries. And I found at my local astronomy shop a really nice holder and spider set up for a 2.55" secondary (which they also supply). A quick calculation at the shop showed that this was a 19.5% CO by diameter which is good in my books, not too little going on some wild planetary optimization goose chase, not too much as to turn my newt into a low-contrast SCT with diffraction spikes.

So in the real world I found and bought this nice, light totally suitable for my build 2.55" holder and mirror. So now I know that fits in that range Vlad (and Mike and Newt) helped calculate. But seeing Vlad's response to John Bambury one thread below made me wonder if 2.55 is close to my theoretical minium of 2.3 I don't want to see the edges of the diagonal (of course you could paint or tape them over as a last resort), but right now I have a freedom which John doesn't: I am designing and can make my cage diameter anything I want, whereas he is stuck with his tube as is.

I can also position my cage vertically anwhere. So, Vlad, Mike or anyone else care to give me a yea or nay on this one:
Given a 13.1" D and FL of 58.5" f/4.46 and diagonal (real) of 2.55" and focuser hole of 2"

what should be my ID of my upper cage assuming that I am not doing any secondary offset, just a centered secondary. I was thinking 14" with a .25" focuser board. Still sound good? I was also thinking of making a 1/4" filter slide with the one 2" hole being filter free which would be on the inside of the ID and could act as a baffle if that is a consideration?

Thank you (all) !!!! You're so helpful!

Tom L

Zoiks! Apple ply is twice as expensive as BBB grade baltic birch. Is it twice as good? BBB means one side is free of plugs and the other may have some, but few. Opinions?

Somehow a seed pod from a backyard tree is now on the mirror of my Intes MK67. I doubt if it's causing light loss per se, but it bothers me that it's there. It's only about 1/8" diameter, and I would be happy if I could knock it off and over to the gap between the mirror and the wall of the OTA, but it seems to want to stick to the mirror which makes me think it will eventually eat the coating there. Am I better off trying to knock the OTA until the thing does fall into the gap or is there a safe way to take the corrector off and pick it off the mirror and reset the corrector without hurting collimation or the matching of the corrector to the primary?

Thanks.
Tom.

Somehow a seed pod from a backyard tree is now on the mirror of my Intes MK67. I doubt if it's causing light loss per se, but it bothers me that it's there. It's only about 1/8" diameter, and I would be happy if I could knock it off and over to the gap between the mirror and the wall of the OTA, but it seems to want to stick to the mirror which makes me think it will eventually eat the coating there. Am I better off trying to knock the OTA until the thing does fall into the gap or is there a safe way to take the corrector off and pick it off the mirror and reset the corrector without hurting collimation or the matching of the corrector to the primary?
Thanks.
Tom.