Jump to content

Stargazers Lounge Uses Cookies

Like most websites, SGL uses cookies in order to deliver a secure, personalised service, to provide social media functions and to analyse our traffic. Continued use of SGL indicates your acceptance of our cookie policy.

sgl_imaging_challenge_banner_android_vs_ios_winners.thumb.jpg.803608cf7eedd5cfb31eedc3e3f357e9.jpg

brianb

Members
  • Content Count

    4,330
  • Joined

  • Last visited

Everything posted by brianb

  1. Tried varifocals, whanging headache all the time ... even bifocals are a nuisance, cause me balance issues & make it very hard to judge distance.
  2. Try the "shadows & highlights" tool in Photoshop Elements - I find the default setting works very well. Trick - no - try turning the gamma right down & the gain right up so you get the shortest possible exposure & the most contrasty image available to focus on. Then drop back to "sane" settings to actually take the movie. But focusing is never easy, and time spent doing it is never wasted.
  3. The active area numbering is a consecutive scheme running back many years. Some sites drop the 10,000s digit as there is no risk of confusion.
  4. Ummm ... so why is the Ace unsuitable if the Flea is? (Same sensor chip ...)
  5. TBH you're far better off getting a current camera modified. The 20D is pretty stone age by the standards of modern cameras ... for a start it WON'T accept EF-S lenses; there's no "live view" & the review screen is horrid by current standards; the ISO range is limited, the software doesn't support FAT32 and therefore there is no way of using CF cards bigger in capacity than 4GB, the noise reduction is primitive (best turn it off) ...
  6. The '21 is best for planets or high magnification closeups of lunar/solar surfaces. The '41 is best for wide area views of the lunar/solar surface. The '31 is a good compromise. Mono is best - because of the freedom to image in the UV or IR - and mono is fine for the moon which has essentially no colour anyway. Solar work really requires a mono camera. The issue with the colour camera is the reduced sensitivity & resolution caused by the Bayer matrix - but the DBK "one shot colour" camera is fine for Jupiter or Saturn - the one to avoid is the DFK, you do NOT want IR blocking built in! A UV/IR blocking filter is a valuable accessory but being forced to use it is Not A Good Thing. There is a '51 camera coming (1600 x 1200 @ 12 fps) I WANT ONE NOW!
  7. So - what's new? Having backed out of Avistack v2 finding 1.81 far superior in all respects except processing time, I'm going to need convincing that it's worth trying ...
  8. Well I don't like polarisers for a variety of reasons, mostly due to the loss of contrast. Of the ND filters, if I could have only one, I'd be torn between the 0.9 & 1.2. 0.6 is definitely too light, 1.8 is definitely too dark & 3.0 is nearly opaque! My preference for a moon filter is Wratten #29 (deep red) but #58 (green) is also acceptable if you don't mind losing dark adaptation.
  9. A good scope will last a lifetime but eyepieces are subject to accidents (gravity) ...
  10. Yes, I have a 110mm aperture f/7 triplet APO scope with a fluorite element ... like this but the older mode without the digital gauge on the focuser.
  11. The lower corona blends into the chromosphere & the chromosphere is what you're seeing with a Ha scope. But there is a big difference in brightness, the scattered light in a Ha scope will swamp all but the very brightest features even in the inner corona. In this image, as well as the prominence, there is a radial gradient in the "background" - but I wouldn't claim this as inner corona, it's much more likely light scattered in the atmosphere and in the optics. (The solar disk - grossly overexposed - has been coloured black to creat an "artificial eclipse" which shows off the prominence better ... it doesn't look like that in the raw image!) Actually solar Ha filters are complex beasts with lots of surfaces and may therefore be rather less likely to show coronal features than a Lyot coronograph - which does work, if you have an exceptionally good high altitude site to use it from.
  12. brianb

    Haze

    Oh no, just think of the business opportunities for selling oxygen if we had the atmosphere removed ... gotta be economic growth in there somewhere
  13. Horse for courses: For astro work, individual focus. For birding, centre focus.
  14. brianb

    Haze

    Cloud is far more of an issue than haze here. Had about 3 hours "clear" sky since full moon.
  15. That's not quite right ... we're talking fundamental particles rather than atoms. Now, the "quantum foam" which exists at very small scales means that pairs of particles and antiparticles are continually coming into existence and almost immediately annihilating each other - the energy from the annihilation exactly balances that needed to produce the particle-antiparticle pair in the first place, so that on a large scale everything balances itself out. (There was an excellent explanation of this in the programme "Nothing" broadcast on BBC4 last night.) Unless there is an event horizon nearby. Then what happens is that there is a small chance that one of the particle/anti-particle pair will find itself on the other side of the event horizon to its counterpart, so annihilation cannot occur. Though it is still at the bottom of a very deep gravitational well, the sides are no longer vertical, so there is a chance that it can escape from the system. Obviously the more massive the black hole is, the greater the energy needed to escape. But a massive black hole also has a bigger event horizon ... Do the sums and it turns out that the evaporation rate is inversely proportional to the fourth power of the mass of the black hole (i.e. a hole twice as massive takes 16 times as long to evaporate). This is all a bit strange, as the particle that escapes carries energy from the black hole the black hole's mass must decrease, even though it's apparently gained the mass of the particle that didn't escape ... however intuition doesn't count for much in quantum mechanics!
  16. This is controversial & depends on some features of particle physics which are utterly lacking in experimental verification. But it is thought that all particles are fundamentally unstable and will eventually decay, unless they happen to be travelling at the speed of light (in which case the aging process is suspended by application of Lorenzian time dilation). When a particle decays it gives rise to a collection of other particles (possibly none of them) and photons, the other particles are of course subject to decay themselves, so everything eventually degrades to photons - which travel at the speed of light and therefore don't decay. I don't fully understand the theory of particle decay but I believe it is intimately concerned with the weak nuclear force, which also controls the radioactive decay process in atomic nuclei.
  17. Don't know which ones these are ... "white" fluorescent tubes are around 4000K, electronic flash is around 6000K and is noticeably bluish in daylight ... 6500K would be a mix of about 1/2 "white cloud" illuminated by sunlight and 1/2 light from a clear blue sky. You need several mireds colour shift to correct this with daylight balanced colour film, 81B or 81C filter will do nicely. Of course with digital cameras you don't need the filter, but you still do need to balance the colour at some stage.
  18. Hmmm .... solar photosphere is approx. 5800K, the "sunlight" colour balance on DSLRs is around 5200K - the difference is that much blue light is scattered by the atmosphere. If you set your custom white balance to 6500K and take an image in normal sunlight, it will be noticeably orange hued.
  19. Irrelevant ... think in terms of actual focal length and/or resolution in arc sec /per pixel.
  20. I don't see why ... if you take a circle of pixels within the FHWM of the focused image of the reflection, there will be very little "unwanted" light in there ...
  21. I don't like the idea of using a diffuser, there's bound to be some spectral shift. Why not just use the reflection of the sun in a ball bearing? It doesn't matter whether the sun is "white" or not, so long as the colour is the same. (Same balance of red / green / blue of the pixels within the disc representing the star's image.) Calibration should help you get this right. And G2V is a fairly coarse specification - there is a small spread of photospheric temperatures in the continuum between what would be G1V and what would be G3V, and the metallicity of the photospheric composition can vary quite a lot depending on when & where the star formed. The effect on colour balance is not large, probably you wouldn't be able to detect it by eye even if you have exceptionally good colour vision.
  22. Saturday March 26th: The Sun has many spots visible in white light; there are five active areas in the eastern sector (plus a very small sixth near the west limb). 2011 Mar 26, 1055 UT. WO FLT 110, Lunt solar wedge, ND 3.0 & Wratten 29 (deep red) filters, prime focus, DMK41; 80% resize. Here's a closeup of the main active area (AR 11176): 2011 Mar 26, 1038 UT. WO FLT 110, Lunt solar wedge, ND 3.0 & Wratten 29 (deep red) filters, 3x tele-extender, DMK21. And here's the main activity (south of the solar equator) in hydrogen alpha: 2011 Mar 26, 1119 UT. WO FLT 110, Solarscope SF-100 Ha filter set, 2x Powermate, DMK41: 2 frame mosaic, 55.5% resize; full size version here.
  23. That sounds about par for the course. Look down the back of your sofa, it's amazing what accumulates in there.
×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.