[ejbpesca]

I am looking towards buying a 180mm or so prime telephone lens for my DSLR.

I do know from this site that Sigma produces the resolution I want as compared to Vivitar but what about Tamron? Would Tamron be up there with Sigma or down there with Vivitar for producing tack sharp images on a computer screen after a photo is taken at 18mp and 24mm sensor? I sure like the Tamron price compared to Sigma but have no comparison unless you can steer me towards on or just give your opinion.

One other question please. Does Pentax make lenses that fit other brands of cameras? I do own two Pentax cameras but one is 35 years old and the other even though fairly new...the x90 was discontinued right after I bought it! It of course cannot produce the results I am now looking for due to small sensor size and being a zoom cam. I am wanting that freak out sharpness the eye cannot see without a camera lens taking the image to medium first.

Thanks in advance....standing by.

[demp10]

for producing tack sharp images on a computer screen after a photo is taken at 18mp and 24mm sensor?

Do you plan to crop the images?

A good computer screen is about 2mp so unless you are cropping the 18 or 24mp image, you are reducing it by a big factor loosing most of the fine details that you'll get from a great lens. You can always zoom in while viewing the image, but then you will not be seeing the full frame you shot.

Almost any digital camera/lens combination can produce great results at 2mp for viewing to a screen.

Instead of focusing on sharpness alone, you should consider several other factors that influence a good photograph. Some will be, how fast is the lens, Bokeh, resistant to flares and ghosts, contrast, color rendition and saturation, minimum focus distance, weight, construction, and many more.

[ejbpesca]

Yes, I will be cropping the photos. I will use cropping like a "post zooming". I understand zooms in my price range, and I have owned several cheap ones cause noise. Noise is the enemy I seek to eliminate and resolution to a computer screen is most important, not to paper printing.

What I'm looking for I have seen produced on the computer screen and I am hoping by the above described lens I will finally be there. Sigma produces what I want, I will see if Tamron comes close.

[demp10]

If noise is your main concern, and by noise you refer to sensor noise (e.g. high ISO), then a lens will not help on that since all of the noise is generated by the sensor. Different cameras have significantly different noise figures especially on high ISO with the K-5 at the top.

Having said that, if you have a fast lens and the shotting situation allows using a wide open aperture (e.g. DOF is not important) then you can use lower ISO (with much less noise) to shoot the same scene, so essentially reducing the overall noise.

There are plenty of noise-reduction software that can dramatically improve a noisy image. Good lighting and exposure also helps a lot. In most cases over exposing is preferred to under exposing. By digitally increasing the exposure you also increase the noise.

[ejbpesca]

When you speak of a "fast" lens. Are you referring to the maximum opening size of the aperture?

[demp10]

When you speak of a "fast" lens. Are you referring to the maximum opening size of the aperture?

Yes, a lens that has a wide open (smallest number) aperture of F2.8 is faster (allows more light to pass trough) than a lens that has F5.6.

So if you have two lenses, one that can be opened to F2.8 and another at F5.6, the F2.8 is 2 stops faster. If the proper exposure with the F5.6 was Shutter Speed = 1/100, F=5.6 and ISO = 800, you can make the same exposure with the faster lens at Shutter Speed = 1/100, F= 2.8, and ISO = 200, which will give you considerably less noise.

Of course you can lower the shutter speed with the F5.6 lens to 1/25 and still use 200 ISO, but unless you are using a tripod, you will introduce camera shake (depending on the focal length) that will make the resulting image noise free, but blurry.

[ejbpesca]

Photog 101. Yep, coming back to me now. I think I have chosen the best lens for the money f 3.5 and 180mm prime. It should get me up close, low noise, low blur, and with the 18 mp camera, just maybe I can pull out a portion of the shot as if I were zooming in on it without much loss of resolution. That is the plan. Equipment will be here today.