AMATEUR PHOTOGRAPHY. 



65 



the negative. ' It is needless to say that the 

 results they obtain are not always of the 

 highest class. When developing paper was 

 first introduced I tried it, using the carbon 

 grade. I gave it up in disgust, as the re- 

 sulting prints were poor. I tried the paper 

 at intervals for a year or 2, with indifferent 

 success, until T happened to get hold of a 

 package of quicker working paper, known 

 as the portrait grade. From that time 

 on I have used developing work almost 

 exclusively for my ordinary paper, and 

 have tried most of the brands on the mar- 

 ket. Nearly all are good when rightly 

 handled, but care is needed in working 

 them if success is looked for. I keep on 

 hand 4 or 5 grades of different speeds and 

 surfaces, and there is always some one of 

 these that is preeminently the best for use 

 with a particular negative. 



To realize how many different effects are 

 possible from one negative one must try 

 it with different grades of paper. This I 

 strongly advise the progressive amateur to 

 do. Once he understands what an import- 

 ant means for improving his work is thus 

 placed in his hands, he will no longer be 

 content to use one grade of paper for ah 

 work, but will keep at hand a supply of the 

 various grades, so he may test- each nega- 

 tive as it is made and make his final print 

 on the paper best suited to its character. 

 C. M. Whitney, Bayonne, N. J. 



THE HYDROMETER TEST. 



The hydrometer used by photographers 

 has a different scale from the standard 

 hydrometers for taking the specific gravity 

 of fluids as used by chemists, and is called 

 the photographer's hydrometer or actino- 

 meter. Whenever the directions for com- 

 pounding any developing or other photo- 

 graphic solution say "by hydrometer test," 

 it is intended that this special photog- 

 raphers' actinometer should be used and not 

 the standard hydrometer. 



The actinometer scale indicates the num- 

 ber of grains of silver nitrate to the ounce 

 of water. For example, in a solution of 

 silver nitrate 10 grains to one ounce of 

 water, the actinometer would read 10. In 

 the same solution the standard hydrometer 

 would read 1.019. For ordinary purposes 

 it is sufficiently accurate to count 2 points 

 on the standard hydrometer scale for each 

 point on the actinometer scale, if one wishes 

 to find the relative value of a reading of one 

 instrument on the other. For accurate 

 readings the fluids to be tested should be 

 at a temperature of 60 deg. F. The 

 chief advantage of using the actinometer 

 for making solutions is its accuracy. Solu- 

 tions can always be made just alike, no 

 matter whether the chemical, say sodium 



sulphite, for instance, is in crystals, dry 

 anhydrous or granular form. It is not ne- 

 cessary to change the quantities for the 

 different forms as it is when we weigh 

 them. Just keep adding the sulphite until 

 the required reading on the scale is reached. 

 Another advantage is the convenience of 

 the actinometer and the quickness with 

 which solution can be made. I buy my 

 sodium sulphite and sodium carbonate in 

 5-pound bottles,- getting the C. P. crystals, 

 as the crystals dissolve better than the 

 anhydrous form. As soon as I get a new 

 supply I fill the bottles with water and add 

 water as I use the solution ; so I always 

 have a saturated solution on hand from 

 which any strength of solution can be made 

 in a few minutes by adding water. 



R. L. Wadhams, Wilkes-Barre, Pa. 



Please compare the F system of stops 

 with the universal. If the exposure was 

 one second with the F system (largest stop) 

 would the exposure be 2 seconds with the 

 next succeeding stop and so on? 



Please explain the F system. Why is it 

 different from the universal? 



H. E. Roberts, New Castle, Pa. 



There are in common use 2 systems of 

 numbering stops, the F and the uniform. 

 Some lens makers have systems of their 

 own, but nearly all the lenses now use one 

 or the other of these 2. The 2 systems 

 compared are as follows : 



UNIFORM SYSTEM. 



No. 124 8 16 32 64 128 256 

 F. f/4 f/5.6 f/8 f/11.3 f/16 f/22.6 J/32I7477/64 



F SYSTEM. 



For example, take F|8. This means the 

 focal length of the lens divided by 8, but 

 for convenience it is written F|8. In the 

 uniform system each succeeding number is 

 Yz the area of previous one and requires 

 double the exposure. Beginning with No. 1, 

 F|4 was chosen as a starting point. As the 

 light that passes through a stop is propor- 

 tionate to the area of the aperture and the 

 areas of circles are proportionate to the 

 squares of their diamaters it is easy to cal- 

 culate the F value for any number of the 

 uniform system. No. 1 is equal to FI4. To 

 find the value of No. 2, square 4 — 16, 

 then multiply by 2 — 32 and extract the 

 square root = f 5.6; and so on for each 

 succeeding F value. 



With lenses numbered on this basis 

 knowing the exposure for any one stop the 

 exposure for the next larger stop will be 

 Yz and for the next smaller stop twice the 

 known exposure. — Editor. 



