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Forum: Pentax Q 3 Days Ago  
Q7 and 01 lens do Gordon Lightfoot concert
Posted By AstroDave
Replies: 12
Views: 517
Glad to hear he is sounding better. I skipped his local concert a month or so ago because when we heard him in person 3 or 4 years ago, it was almost a painful experience - he did the railroad trilogy pretty much under duress due to demand, and it was not very good. Similarly with The Edmund Fitzgerald.
Forum: Pentax K-70 09-18-2018, 06:56 AM  
Can't figure out how to fine-tune the K-70 internal clock
Posted By AstroDave
Replies: 5
Views: 291
If you need watch time and camera time to be closely synchronized, take a picture of your watch when you start/end a relevant photo session. You can then find the difference between "real" time and camera time.
Forum: Flashes, Lighting, and Studio 09-14-2018, 09:30 PM  
Flash Duration t0.1, t0.5
Posted By AstroDave
Replies: 6
Views: 248
It's not the rise time, it's the area under the light curve - you need to integrate the light curve to get the "power" values. Nobody but me seems to have ever done that. As you say, it's not at all difficult, but you do need a computer program of some sorts along with your scope and other equipment. (Which should be at least a phototransistor (microsecond response time), and ideally a photo diode (nanosecond response time) - a "photocell" (which I take to be an old style selenium, say - millisecond response time) is nowhere near fast enough for this!) You need the individual data points in the light curve. A modern digital storage oscilloscope provides this.

Oh, and no 1 uF cap! Time constant (rc) with a 10k resistor is 0.01 second!
Forum: Flashes, Lighting, and Studio 09-14-2018, 07:14 PM  
Flash Duration t0.1, t0.5
Posted By AstroDave
Replies: 6
Views: 248
t0.1 is the time between when the power level of the flash light value is between 0.1 of the max - from rise to fall of the light curve. Similarly, t0.5 is the time between the half power levels (0.5!) of the peak. This gives you some idea of how long the flash light burst lasts.

In my opinion, these are only somewhat useful numbers. What you really want is the fraction of time that some fraction of the output light power lasts - that's what lights up your subject, and a big deal if things are moving/changing during the flash illumination. I prefer what I call p50 or p90 - the time during which 50% or 90% of the total light output power takes place. These are more difficult to measure than t0.1 and t0.5 - as well as typically less "nice" for the flash manufacturers (i.e. they are LONGER than the p values).

See my measurements for the AFG540FGZ for some real-world results and comments: Flash Duration Measurements - AF-540FGZ -
Forum: Pentax K-1 09-12-2018, 09:38 AM  
K1 II Red color cast in flash photos
Posted By AstroDave
Replies: 19
Views: 725
Even if you set the white balance, be careful - the camera may think it is smarter than you are. You may need to some options(s) in the C menus (C3/15 seems to be the one for the K1 (same for the K1 II? don't have that manual)).

I had a somewhat similar problem with flash white balance a while ago: Wacky white balance with remote trigger studio flashes for K5 -
Forum: Contest Voting 09-09-2018, 08:00 PM  
Making Power
Posted By AstroDave
Replies: 31
Views: 285
I would like to nominate this photo
Forum: Contest Voting 09-09-2018, 08:00 PM  
Night trains
Posted By AstroDave
Replies: 34
Views: 256
I would like to nominate this photo
Forum: Contest Voting 09-09-2018, 07:59 PM  
Invisible tracks
Posted By AstroDave
Replies: 26
Views: 254
I would like to nominate this photo
Forum: General Photography 09-07-2018, 07:22 PM  
Purposely out of focus
Posted By AstroDave
Replies: 94
Views: 2,086
Here are a couple of my out-of-focus pictures (both on purpose!)

The first is of water drops on the front steps

The second is some zoomed parking lot lights at night (used for an example of night shots for the photo class I was teaching)
Forum: Pentax K-70 09-02-2018, 08:19 PM  
Posted By AstroDave
Replies: 2
Views: 279
Taktoon's shooting values and suggestions are right on. In particular, pay attention to focus. Put your exposure dial on M and use manual focus! You may want to use live view on the first few launches while you get focused.

Here are some fireworks shots I took two year’s ago at Niagara Falls from the Canadian side (they have a nice show a couple of evenings a week during the summer and early fall).

I started at ISO 200 and f/11, and decided that 6-second exposures were adequate. Assuming it is dark enough, you can use almost any exposure length - just about the only thing you will see are the fireworks and the brightest stuff in the background. You want exposures long enough to show the launch trail, burst, and subsequent spread of the firework(s). Depending on the launch rate, you may get several bursts in one frame. If you want more events in an image, you can combine shots in post.

Since I was traveling on vacation, I did not have a tripod, but held the camera (K-1 with 28-105 lens) firmly on a stone rail post. The resultant images were tipped a bit since the rail top was not quite level, but that’s easily fixed in post processing. I’ve “leveled” the images shown here, but otherwise NO adjustments have been made to exposure - these are cropped jpegs straight from the camera. I was using manual white balance, but have no recollection of how I set it - I think the WB is close to daylight.

I find this first picture to be a bit bright. It shows nicely the launch trail and smoke that accompanies a typical fireworks show, but the burst itself is very close to overexposed.

After that, I lowered the ISO to 100 and stopped down a bit. The last three shots are at f/13, f/13, and f/16 . I think they are better at showing the fine detail in the bursts, with only the burst centers overexposed. Given the dynamic range of the K-1, they can be brightened if desired to show smoke and other fainter details in and around the show.

Get out there and experiment!

Forum: Pentax Forums Giveaways 09-02-2018, 06:00 AM  
August Pentax K-1 II Giveaway: Raffle Thread 2, 13:00 UTC, September 2, 2018
Posted By AstroDave
Replies: 80
Views: 1,947
Here's the winner!
Forum: Film Processing, Scanning, and Darkroom 08-30-2018, 03:11 PM  
What is your favirte film emulsion?
Posted By AstroDave
Replies: 14
Views: 412
If you sent me to a desert island, I'd hope that somehow some Kodachrome could accompany me. Guess I'd need a development lab to join me!
Forum: Pentax SLR Lens Discussion 08-29-2018, 03:49 PM  
Pentax AF Adapter!!!
Posted By AstroDave
Replies: 24
Views: 734
Yes - the 1.7 AF teleconverter: SMC Pentax-F 1.7x AF Adapter Reviews - Pentax K-mount Teleconverters and Adapters - Pentax Lens Reviews & Lens Database

Once you get close to proper focus with the main lens, the 1.7 adjusts its own internal lenses to fine tune the focus, using the screw drive focus system of the camera.

I have one. It is rather nice in action.
Forum: Pentax Forums Giveaways 08-29-2018, 06:16 AM  
Pentax Giveaway "What will you do if you win?"
Posted By AstroDave
Replies: 180
Views: 2,605
Quite feasible, actually (at least here in the US at the moment)

for bodies only, priced at B&H a few minutes ago:

price of KP: $870 (claimed to be $200 off)

price of K-1 MkII: $1897 (claimed to be $100 off)

Thus a pair of KPs would set you back just $1740. You’ll have $150 left over for a cheap lens.

Better act fast, though - pricing claimed to be good only until August 31 - before the camera raffle, I’m afraid - so plan ahead if you are going to be the winner!!!
Forum: Pentax K-70 08-27-2018, 01:01 PM  
Pentax f 100 - 300mm lens
Posted By AstroDave
Replies: 8
Views: 393
This lens? SMC Pentax-F 100-300mm F4.5-5.6 Reviews - F Zoom Lenses - Pentax Lens Reviews & Lens Database

It should work fine with your K-70 - when everything is set properly.

Have you read the manual? This can be somewhat daunting, but also very useful! Page 121 tells you what and how lenses are compatible with the K-70. If you have the lens reviewed above, do you have the aperture ring set in the A position? That is probably the best place to start until you get more familiar with your camera.

Is your camera set for autofocus or not? That can effect whether the shutter will fire. Look at p.61 in the manual. Are you getting a focus "beep"? (page 46)

What camera mode are you using: Auto, P, Sv, Tv or something else? Auto with the lens set to A and making sure the camera is set for autofocus should get you some pictures.

Do you have a data card in the camera? Nothing happens without that!!
Forum: Photographic Technique 08-26-2018, 04:37 PM  
Astro Beginners guide to shooting the moon
Posted By AstroDave
Replies: 16
Views: 611
Nice info, but I like UncleVanya's f8 a bit better. The moon is fairly dark, especially compared to the earth (for which "sunny 16" was formulated).

A bit more on focusing on the moon: if you are lucky/careful, and depending on your focal length, you may be able to focus directly on the center of the moon or wherever it is lit up (using center spot focus, of course!). If that doesn't work, try the illuminated edge - that's about as contrasty as you can get, which the autofocus system likes.

I prefer using magnified live view for the final touch up, with manual focus selected.

As noted, use a tripod if at all possible.
Forum: Pentax SLR Lens Discussion 08-24-2018, 07:20 AM  
Film Travel Kit - Lens Suggestions
Posted By AstroDave
Replies: 18
Views: 512
Sounds embarrassingly familiar! That was me and my ME for 30 years or so. Now I've got half a dozen digitals and 15-20 lenses!!
Forum: Photographic Technique 08-23-2018, 11:04 AM  
Real estate exercise, which lens(es)?
Posted By AstroDave
Replies: 19
Views: 568
You can practice at home - bathrooms and other small rooms will be the big challenge. You want to be able to get nearly ALL of a room in a single shot. So, As boriscleto suggests, you are going to want a wider (non-fisheye IMO) lens.

Use a tripod. Since you can then do long exposures, you may not need all your lights. Use high f-stops for depth of field (but not so high that you get killed by diffraction - but see pixel count comment below. F11 or even F16 should be fine with APS-C, and 16 or 22 should be fine with full frame). Do a custom white balance!

MAKE SURE YOUR CAMERA IS LEVEL. This is the best way to get straight vertical lines with no post-processing. Be prepared to throw away the bottom half of most of your frames. You probably have way more pixels than you need, since your pictures will probably be headed on-line, where 1920 by 1080 or less will be the pixel size.
Forum: Troubleshooting and Beginner Help 08-20-2018, 06:52 PM  
Lens size restrictions at Racetrack
Posted By AstroDave
Replies: 21
Views: 756
A Q7 with the adapter for K-mount lenses (get the real Pentax one!) can give you a lot of reach. I had a similar problem at an NFL exhibition game. A 100 macro (f 2.8) on a Q7 is like a 500mm or so telephoto and the gate keepers will have no idea what you have.
Forum: Pentax DSLR Discussion 08-16-2018, 02:40 PM  
Fun thread: If you were given $5,000 to spend...
Posted By AstroDave
Replies: 163
Views: 3,487
Happy with my cameras (K-1 and K-3), so I guess I would buy the 150-450 zoom and all the new FF 2.8 zooms (15-30, 24-70, and 70-200) - and now I'm a thousand bucks in the hole (and have an aching back from carrying it all)!

Looks like Norm and I are in the same boat (er, canoe?).
Forum: Pentax SLR Lens Discussion 08-15-2018, 07:37 PM  
question on tele conveter lenses
Posted By AstroDave
Replies: 18
Views: 687
I've triple-stacked TCs - on the sun - PLENTY of light: Magnification Factors for several Kenko Teleconverters on K5 -

The results weren't too bad, and certainly better than trying to upsample in this case.
Forum: Troubleshooting and Beginner Help 08-12-2018, 08:53 AM  
Sensor Dust or No Sensor Dust?
Posted By AstroDave
Replies: 16
Views: 971
IF you do find that you actually have some dust, before you go sensor swabbing, try blowing it away.

The general consensus for a blower seems to be the Giotto Rocket Blower (at Adorama or B&H), but I'm a cheapskate and find that my wife's turkey baster works perfectly well. (Make sure there's no residual gravy grease from last Thanksgiving!!)
Forum: Pentax Full Frame 08-11-2018, 03:34 PM  
K1 Continuous Shooting Color Shifts
Posted By AstroDave
Replies: 15
Views: 666
Be aware of #15 under the custom setting C3 menu "WB Adjustable Range" too.

Even if you have chosen a specific white balance, the camera may think it is smarter than you are and adjust it anyway. I had this happen to my K5 when shooting flash - I'd get changes in the background (a redness variation) very similar to your effect:

Wacky white balance with remote trigger studio flashes for K5 -

Drove me nuts until I figured it out! Seems to me that when you set the white balance, the camera shouldn't diddle it.
Forum: Troubleshooting and Beginner Help 08-10-2018, 12:51 PM  
Pentax K10D strange noise?
Posted By AstroDave
Replies: 5
Views: 286
You probably have the dust removal function set to run each time the camera is turned on. This shakes the sensor a bit to dislodge dust - that's what you hear and feel.

Check out the manual if you don't have it already:
Forum: Monthly Photo Contests 08-09-2018, 08:10 PM  
Summer on Clear Creek
Posted By AstroDave
Replies: 12
Views: 144
I would like to nominate this photo
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